If you are searching for “occurred or occured,” the answer is simple: “occurred” is the correct spelling.
“Occured” is a common spelling mistake. It looks very close to the correct word, so it is easy to type by accident. The difference is only one letter, but that letter matters in standard English.
The correct form is:
“occurred”
The incorrect form is:
“occured”
The word “occurred” is the past simple and past participle form of the verb “occur.” Dictionaries such as Cambridge and Merriam-Webster list “occurred” as the standard form.
This guide explains everything you need to know about occurred or occured, including the meaning, spelling rule, grammar, pronunciation, examples, common mistakes, related misspellings, and practical ways to remember the correct form.
It also covers search variations such as “ocurd,” “ocurred,” “occurd,” “occurredd,” “occurrred,” “occuried,” “occurrd,” and “ocurrred.” These are not standard spellings, but they are useful to understand if you are checking a spelling mistake or researching what people mean when they type an incorrect version into a search engine.
Quick Answer: Occurred or Occured?
The correct spelling is:
“occurred”
The incorrect spelling is:
“occured”
Here is the easiest comparison:
| Spelling | Correct? | Meaning |
| occurred | Yes | Past form of “occur” |
| occured | No | Common misspelling |
| ocurred | No | Missing one c |
| occurd | No | Missing e |
| occurrd | No | Missing e |
| occurredd | No | Extra d |
| occurrred | No | Extra r |
| occuried | No | Incorrect word ending |
| ocurrred | No | Incorrect number of r’s |
| ocurd | No | Multiple letters missing |
If you are writing for school, work, a website, a report, or any professional purpose, use “occurred.”
What Does Occurred Mean?
“Occurred” is the past tense and past participle of “occur.”
The most common meaning is “happened” or “took place.”
For example:
“The accident occurred yesterday.”
This means:
“The accident happened yesterday.”
Merriam-Webster defines “occur” in several ways. It can mean to be found or present, to come into existence or happen, or to come to mind.
For example:
“The accident occurred at noon.”
Here, “occurred” means “happened.”
Another example is:
“It occurred to me that I had forgotten my wallet.”
Here, “occurred to me” means that an idea came into my mind.
The word can also describe something naturally existing in a location:
“The plant occurred naturally in the region.”
In this sentence, “occurred” means that the plant was found or existed there.
Why Is Occurred Correct?
The spelling comes from the base verb “occur.”
The base word is:
occur
When it becomes the past tense, the final “r” is doubled before the “-ed” ending:
occur → occurred
The result contains two c’s and two r’s:
o-c-c-u-r-r-e-d
Merriam-Webster specifically notes that the r is doubled in the past tense “occurred” and remains doubled in the present participle “occurring.”
This is why “occured” is missing an important letter.
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Correct:
occurred
Incorrect:
occured
Why Do People Write Occured?
“Occured” is a very common spelling mistake because the word is not easy to spell from pronunciation alone.
When people say “occurred,” the two r’s are not always obvious. A writer may remember the basic word “occur” but then add “-ed” without doubling the final r.
That produces:
occur + ed = occured
But standard spelling requires:
occur + red = occurred
The correct word therefore has:
- Two c’s
- Two r’s
- One e
- One d
The unusual-looking combination of repeated letters makes “occurred” easy to misspell.
Occurred Has Two Sets of Double Letters
One useful way to remember the spelling is to notice that “occurred” contains two sets of repeated consonants.
It begins with:
cc
and contains:
rr
So the structure is:
occ + urr + ed
This produces:
occurred
Grammarly also explains the spelling by pointing out the double consonants in “occurred.”
A simple memory trick is:
“Occurred has two c’s and two r’s.”
That is often enough to prevent the common “occured” mistake.
Is Occured Ever Correct?
No.
“Occured” is not the standard spelling of the past tense of “occur.”
If you are writing in standard American English, use “occurred.”
For example:
Incorrect:
“The problem occured yesterday.”
Correct:
“The problem occurred yesterday.”
Incorrect:
“The accident occured at 8 p.m.”
Correct:
“The accident occurred at 8 p.m.”
Incorrect:
“It occured to me later.”
Correct:
“It occurred to me later.”
There is no normal grammatical situation where “occured” should replace “occurred.”
Occurred in American English
For readers in the United States, “occurred” is the standard spelling.
American English uses:
- occur
- occurs
- occurred
- occurring
- occurrence
The spelling “occured” is not an American English alternative. It is simply a misspelling.
This matters because people sometimes wonder whether “occured” might be an acceptable regional spelling. It is not.
The same standard spelling is used in other major varieties of English as well.
Occurred in British English
British English also uses “occurred.”
For example:
“The incident occurred yesterday.”
The spelling does not change to “occured” in British English.
This makes “occurred” one of those words where American and British English agree.
Grammar of Occurred
“Occurred” has two main grammatical uses.
First, it is the simple past form of “occur.”
Example:
“The accident occurred last night.”
Second, it is the past participle of “occur.”
Example:
“The accident has occurred before.”
Cambridge Dictionary identifies “occurred” as both the past simple and past participle form of “occur.”
Understanding this distinction can help you use the word correctly in longer sentences.
Occurred as the Simple Past
Use “occurred” when something happened at a completed time in the past.
Examples include:
“The meeting occurred on Monday.”
“The accident occurred during the night.”
“The error occurred after the update.”
“The change occurred several years ago.”
“The earthquake occurred in the early morning.”
In all of these sentences, the event has already happened.
Occurred as a Past Participle
“Occurred” can also be used after helping verbs such as “has,” “have,” and “had.”
Examples:
“The error has occurred several times.”
“Several changes have occurred since then.”
“The problem had occurred before the technician arrived.”
This form is grammatically different from a simple past sentence, but the spelling remains exactly the same.
Occurred vs Happened
One of the easiest ways to understand “occurred” is to compare it with “happened.”
In many sentences, they have almost the same meaning.
For example:
“The accident occurred yesterday.”
“The accident happened yesterday.”
Both sentences are understandable and grammatically correct.
Merriam-Webster lists “happened” among the synonyms of “occurred.”
However, there is a small difference in style.
“Happened” is usually more conversational.
“Occurred” often sounds more formal or neutral.
For example:
“What happened?”
sounds very natural in everyday conversation.
“What occurred?”
sounds more formal.
This is why “occurred” is common in reports, academic writing, technical documents, and official communication.
When Should You Use Occurred?
Use “occurred” when you need to describe something that happened in the past.
Common situations include:
- An accident
- An event
- A problem
- An error
- A change
- A delay
- A discovery
- A historical event
- A technical failure
- A natural event
- An idea coming to mind
- Something existing in a particular location
Examples:
“The delay occurred because of bad weather.”
“The error occurred during installation.”
“The event occurred earlier than expected.”
“A major change occurred after the policy was updated.”
“The plant occurred naturally in the area.”
Common Examples of Occurred
Here are several simple sentences.
“The accident occurred at approximately 6 p.m.”
“The problem occurred during the final test.”
“The error occurred while the program was running.”
“The meeting occurred as planned.”
“The change occurred gradually.”
“The event occurred more than ten years ago.”
“The storm occurred during the night.”
“It occurred to me that I had forgotten my appointment.”
“The species occurred naturally in the region.”
These examples show that “occurred” has several useful applications.
Occurred in Formal Writing
“Occurred” is especially common in formal writing.
A business report might say:
“The system failure occurred during routine maintenance.”
A school report might say:
“The historical event occurred during the nineteenth century.”
A scientific paper might say:
“The chemical reaction occurred after the solution was heated.”
A technical document might say:
“An unexpected error occurred during installation.”
A news article might say:
“The incident occurred shortly before midnight.”
The word is useful because it is clear, neutral, and professional.
Occurred in Academic Writing
Students may encounter “occurred” frequently in history, science, research, and social studies.
For example:
“The event occurred before the beginning of the war.”
“The reaction occurred after the temperature increased.”
“The change occurred during the second phase of the experiment.”
“Several important developments occurred during this period.”
Using the correct spelling is important in academic writing because repeated spelling errors can make otherwise strong work look less polished.
Occurred in Business Writing
Business professionals also use “occurred” when explaining problems, delays, or events.
For example:
“The delay occurred because of a technical issue.”
“The error occurred during the data transfer.”
“The incident occurred before the scheduled meeting.”
“The change occurred after management approved the proposal.”
In a professional report, “occurred” can sound more neutral than “happened.”
Occurred in Technical Writing
Technology is another area where the word appears frequently.
Software messages often use phrases such as:
“An error occurred.”
This is a standard construction.
You may also see:
“An unexpected error occurred.”
“An error occurred while saving the file.”
“An error occurred during installation.”
“The problem occurred after the system restarted.”
These examples explain why people who work with computers may encounter the word often.
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“It Occurred to Me” Meaning
The phrase “it occurred to me” has a special meaning.
It means that an idea, thought, or realization came into someone’s mind.
For example:
“It occurred to me that I had left my keys at home.”
This means:
“I suddenly realized that I had left my keys at home.”
Another example:
“It never occurred to me that the store would be closed.”
This means that the possibility had never entered the person’s mind.
Merriam-Webster includes “to come to mind” as one of the meanings of “occur.”
This expression is very common in American English.
Occurred Naturally Meaning
Another common use appears in science and nature.
For example:
“The mineral occurred naturally in the soil.”
This means the mineral was naturally present in the soil.
Similarly:
“The species occurred naturally in the region.”
Here, “occurred” refers to something being found or existing in a particular place rather than simply describing an event.
Merriam-Webster includes “to be found or met with” as one meaning of “occur.”
Occurred vs Occurrence
“Occurred” and “occurrence” come from the same word family.
“Occurred” is a verb form.
Example:
“The event occurred yesterday.”
“Occurrence” is a noun.
Example:
“The event was an unusual occurrence.”
The difference is important.
You use “occurred” to describe an event.
You use “occurrence” to name or discuss the event itself.
Other forms include:
- occur
- occurs
- occurred
- occurring
- occurrence
Learning these together can make English vocabulary easier.
Occurred vs Occurring
“Occurred” describes something that happened.
“Occurring” describes something that is happening or taking place.
Compare:
“The problem occurred yesterday.”
“The problem is occurring now.”
Another example:
“The error occurred during installation.”
“Errors are occurring during installation.”
The first sentence refers to a completed event.
The second refers to an ongoing situation.
Merriam-Webster lists “occurred” and “occurring” as forms of “occur.”
Why “Ocurred” Is Incorrect
“Ocurred” is another common spelling mistake.
It has only one c.
Correct:
occurred
Incorrect:
ocurred
The word “occur” already contains two c’s, and the past form keeps those two c’s while also doubling the final r.
Therefore:
o-c-c-u-r-r-e-d
is correct.
“Ocurred” is missing one c.
Why “Ocurred” Appears in Searches
People may type “ocurred” because they remember the word has a repeated sound but do not remember exactly which letter is doubled.
This is a spelling mistake, not an alternative form.
If you see “ocurred” in a search query, the intended word is usually “occurred.”
For SEO purposes, it can be useful to understand this search behavior. However, writers should not repeatedly place incorrect spellings throughout an article just to attract searches.
The priority should be useful, accurate information.
Why “Occured” Is Incorrect
“Occured” has two c’s but only one r.
Correct:
occurred
Incorrect:
occured
The missing r is the key problem.
Remember:
occur → occurred
not:
occur → occured
This is probably the most common spelling error associated with the word.
Why “Occurd” Is Incorrect
“Occurd” is missing the letter e.
Correct:
occurred
Incorrect:
occurd
The ending is:
-ed
not:
-d
Therefore, the final letters are:
r-r-e-d
This makes “occurd” an incorrect spelling.
Why “Ocurd” Is Incorrect
“Ocurd” contains several missing letters.
It does not have the two c’s from “occur,” and it also does not have the correct “-ed” ending.
Correct:
occurred
Incorrect:
ocurd
This form may appear when someone types quickly or tries to shorten the word based on pronunciation.
Why “Occurrd” Is Incorrect
“Occurrd” has the double r but is missing the e.
Correct:
occurred
Incorrect:
occurrd
The correct final sequence is:
rr + ed
which gives:
rred
However, the full spelling must still include the e:
occurred
Why “Occurredd” Is Incorrect
“Occurredd” has an extra d.
Correct:
occurred
Incorrect:
occurredd
There is only one d at the end of “occurred.”
The word ends:
-ed
not:
-edd
This is a simple typing error.
Why “Occurrred” Is Incorrect
“Occurrred” contains three r’s.
The correct spelling contains two r’s.
Correct:
occurred
Incorrect:
occurrred
Think of the base word:
occur
It ends in one r.
When the r is doubled, there are two r’s total.
There is no need for a third r.
Why “Ocurrred” Is Incorrect
“Ocurrred” combines two errors.
It has only one c but too many r’s.
Correct:
occurred
Incorrect:
ocurrred
When you remember the double-letter pattern, the correct form becomes easier:
cc + rr
Therefore:
occurred
Why “Occuried” Is Incorrect
“Occuried” is not the past form of “occur.”
Some English verbs change their spelling when forming the past tense, but “occur” does not change into “occuried.”
The correct form is:
occurred
For example:
Incorrect:
“The accident occuried yesterday.”
Correct:
“The accident occurred yesterday.”
The verb simply takes the appropriate past-tense form with the doubled r.
Related Keyword: Occurd
“Occurd” is a misspelling of “occurred.”
If you are checking a sentence that contains “occurd,” replace it with “occurred.”
For example:
Incorrect:
“The problem occurd during testing.”
Correct:
“The problem occurred during testing.”
The same rule applies to the related variant “occurd.”
Related Keyword: Occurred
“Occurred” is the correct spelling and the primary word discussed in this guide.
It is the past tense and past participle of “occur.” Cambridge Dictionary confirms this grammatical form.
Related Keyword: Ocurred
“Ocurred” is an incorrect spelling of “occurred.”
The difference is the missing second c.
Correct:
occurred
Incorrect:
ocurred
If a spelling checker identifies “ocurred,” it should be changed to “occurred.”
Related Keyword: Occurred
The spelling “occurred” is correct.
If you are unsure whether to write “occurred” or “occured,” always select “occurred.”
Related Keyword: Occurrred
“Occurrred” is incorrect because it contains an extra r.
Correct:
occurred
Incorrect:
occurrred
The correct word has exactly two r’s.
Related Keyword: Occurredd
“Occurredd” is incorrect because it has two d’s.
Correct:
occurred
Incorrect:
occurredd
The correct spelling ends with only one d.
Related Keyword: Occuried
“Occuried” is an incorrect past-tense spelling.
The correct word is:
occurred
Do not change “occur” to “occuried.”
Related Keyword: Occurrd
“Occurrd” is another spelling error.
It has the correct double r but leaves out the e.
Correct:
occurred
Incorrect:
occurrd
Related Keyword: Ocurd
“Ocurd” is also incorrect.
It leaves out important letters from the standard spelling.
Correct:
occurred
Incorrect:
ocurd
Related Keyword: Ocurred
“Ocurred” is another misspelling that may appear in online searches.
It should be corrected to:
occurred
The correct form has two c’s.
Related Keyword: Ocurrred
“Ocurrred” is incorrect because it combines a missing c with an extra r.
Correct:
occurred
Incorrect:
ocurrred
Related Keyword: Occurred vs Occured Search Intent
The search query “occurred or occured” has a clear informational purpose.
Most people who search it want to know:
- Which spelling is correct?
- Why is “occured” wrong?
- How do you spell occurred?
- What does occurred mean?
- Is occurred the past tense of occur?
- How many r’s are in occurred?
- How many c’s are in occurred?
- What is the difference between occurred and occured?
- Can occurred be used in a sentence?
A good answer should provide the correct spelling immediately and then explain the grammar.
That is why this article places the direct answer near the beginning.
Search Intent Behind Misspelled Variants
People may also search for:
- ocurred
- ocurd
- occurd
- occurrd
- occurredd
- occurrred
- occuried
- ocurrred
- ocurred
These are spelling variants rather than separate English words.
Search engines often understand that a user who enters one of these forms may actually be looking for “occurred.”
For content creators, this creates an important SEO lesson.
You can explain the variants without pretending that they are correct.
That approach is better for readers and better for content quality than repeating misspellings unnaturally.
Should You Use Misspelled Keywords in SEO Content?
This is an important question for website owners.
If your target keyword is “occurred or occured,” you can use the exact search phrase in a natural heading such as:
“Occurred or Occured: Which Spelling Is Correct?”
You can also explain related misspellings in a dedicated section.
However, you should not fill paragraphs with misspelled words.
For example, this would be poor SEO:
“Occured occured ocurred occurd occurrd occurred occurred…”
It provides no useful information.
A better approach is:
“People sometimes misspell ‘occurred’ as ‘occured,’ ‘ocurred,’ ‘occurd,’ or ‘occurrd.’ These forms are incorrect in standard English.”
That gives search engines context while helping the reader.
How to Remember Occurred Forever
A simple memory technique is:
“Occurred has two C’s and two R’s.”
Look at the word:
occurred
You can divide it visually:
occ + urr + ed
This gives you:
cc + rr + ed
Another helpful connection is:
occur → occurred
The final r is doubled.
You can also remember:
“occurred” looks crowded with double letters.
The unusual appearance is actually useful because it makes the correct spelling distinctive.
A Simple Spelling Exercise
Complete each sentence with the correct word.
- The accident ______ yesterday.
Answer: occurred
- A technical problem ______ during installation.
Answer: occurred
- It ______ to me that I had forgotten my phone.
Answer: occurred
- The change ______ after the meeting.
Answer: occurred
- Several events ______ during that period.
Answer: occurred
This exercise reinforces both the spelling and the grammar.
Correct and Incorrect Sentence Examples
Incorrect
“The accident occured at midnight.”
Correct
“The accident occurred at midnight.”
Incorrect
“The error occurrd during installation.”
Correct
“The error occurred during installation.”
Incorrect
“The problem occurredd after the update.”
Correct
“The problem occurred after the update.”
Incorrect
“The event occuried last year.”
Correct
“The event occurred last year.”
Incorrect
“The change occurrred unexpectedly.”
Correct
“The change occurred unexpectedly.”
Occurred in Everyday English
Although “occurred” is somewhat more formal than “happened,” it is still common in everyday English.
For example:
“What occurred yesterday?”
“Nothing unusual occurred.”
“A problem occurred while we were driving.”
“An unexpected situation occurred.”
However, in casual conversation, many Americans would simply use “happened.”
For example:
“What happened?”
“What happened yesterday?”
This does not make “occurred” unnatural. It simply gives the two words slightly different styles.
Occurred in News Writing
News writing often uses “occurred” because it is neutral and precise.
Examples might include:
“The incident occurred shortly after 10 p.m.”
“The crash occurred near the intersection.”
“The storm occurred during the overnight hours.”
The word allows the writer to describe an event without adding an emotional judgment.
Occurred in Science
Scientists use “occur” and “occurred” to describe processes and events.
Examples include:
“The reaction occurred after heating.”
“The change occurred naturally.”
“The process occurred over several hours.”
“The species occurred in several regions.”
This reflects the broader meanings of “occur,” including happening and being present or found.
Occurred in History
Historical writing frequently uses “occurred.”
Examples:
“The event occurred in 1776.”
“The conflict occurred over several years.”
“The change occurred after the law was passed.”
“Several important events occurred during this period.”
Because historical writing often discusses completed events, the past tense “occurred” is particularly useful.
Occurred in Legal and Official Writing
Official documents may use “occurred” to describe when an incident happened.
For example:
“The incident occurred on the date listed below.”
“The damage occurred before the inspection.”
“The alleged event occurred at the stated location.”
The word itself does not make a statement legally true. It simply describes an event as having happened.
When writing legal documents, facts should be supported by appropriate evidence rather than relying only on wording.
Occurred in Technical Error Messages
Computer users often see “occurred” in error messages.
For example:
“An error occurred.”
This is a common construction because the software is reporting that something happened.
You may also encounter:
“An unexpected error occurred.”
“An error occurred while processing your request.”
“An error occurred while connecting to the server.”
The spelling is always:
occurred
not:
occured
Pronunciation of Occurred
The pronunciation of “occurred” can make spelling difficult because the written double letters are not strongly visible in speech.
The word is commonly pronounced approximately like:
uh-KURD
The stress falls on the second syllable.
Oxford’s dictionary gives the past pronunciation as approximately /əˈkɜːrd/ for the U.S. form.
Because pronunciation does not clearly reveal every written letter, learners should not rely on sound alone when spelling this word.
Origin of the Word Occur
The word “occur” has a long history.
Merriam-Webster traces it to Latin “occurrere,” meaning to run to meet, confront, or present itself to the mind. It entered English centuries ago, with the dictionary giving its first known English use as the 15th century.
The modern word has developed several related meanings.
Today, “occur” can mean:
- To happen
- To be found
- To exist in a place
- To come to mind
The past form of all these uses is “occurred.”
Is Occurred a Formal Word?
“Occurred” is best described as a neutral-to-formal word.
It is perfectly normal English, but “happened” is often more natural in casual speech.
Compare:
“What happened?”
“What occurred?”
The first is more conversational.
The second is more formal.
In a professional report, “occurred” can be a good choice because it sounds objective.
Occurred vs Took Place
“Occurred” can sometimes be replaced with “took place.”
For example:
“The meeting occurred on Monday.”
“The meeting took place on Monday.”
Both can be correct.
However, “took place” is often more natural when discussing scheduled events.
“Occurred” works particularly well when describing an unexpected event, incident, error, or natural process.
Merriam-Webster lists “happened” as a synonym for “occurred,” while “occur” itself is commonly defined as something that happens or takes place.
Occurred vs Transpired
“Transpired” can sometimes be used as a synonym for “occurred,” but it is not always the best replacement.
For basic English, “happened” is usually the easiest alternative.
For example:
“The accident occurred yesterday.”
“The accident happened yesterday.”
Both are simple and clear.
Using unnecessarily difficult synonyms can make writing harder to understand, especially for readers with basic English skills.
Common Mistakes With Occurred
Here are the main mistakes to watch for:
Occured
Missing one r.
Correct: occurred
Ocurred
Missing one c.
Correct: occurred
Occurd
Missing e.
Correct: occurred
Ocurd
Missing several letters.
Correct: occurred
Occurrd
Missing e.
Correct: occurred
Occurredd
Extra d.
Correct: occurred
Occurrred
Extra r.
Correct: occurred
Occuried
Incorrect past-tense formation.
Correct: occurred
Ocurrred
Missing c and adding an extra r.
Correct: occurred
Recognizing these patterns makes proofreading much easier.
A Professional Proofreading Tip
When reviewing a document, search for “occur” and inspect every variation.
For example, use your document’s search feature to look for:
“occur”
This can help you locate:
- occur
- occurs
- occurred
- occurring
- occurrence
- misspelled versions
Then check each sentence.
This is particularly useful in long reports, technical documents, and website articles.
Featured Snippet Answer
If you need a very short answer for a spelling question:
“Occurred” is the correct spelling. “Occured” is incorrect. “Occurred” is the past tense and past participle of “occur,” meaning happened, took place, or came to mind. The correct spelling has two c’s and two r’s.
Frequently Asked Questions About Occurred or Occured
1. Can “occurred” describe something that is still happening?
Usually, no. “Occurred” normally describes something that has already happened. For an event happening now, use “occurring.”
Example:
“The problem occurred yesterday.”
“The problem is occurring now.”
2. Can “occurred” be used for an idea or thought?
Yes. The expression “it occurred to me” means that an idea came into your mind.
Example:
“It occurred to me that I had forgotten the appointment.”
This is one of the established meanings of “occur.”
3. Is “occurred” pronounced differently from “occur”?
Yes. The past form includes the sound represented by the “-ed” ending, although the exact pronunciation may vary slightly by accent. In American English, it is commonly pronounced approximately “uh-KURD.”
4. Is “occurred” a regular or irregular verb form?
“Occur” forms its past tense with “-ed,” so it follows a regular past-tense pattern, although its spelling requires doubling the final r. The standard forms are occur, occurs, occurred, and occurring.
5. Can I use “occurred” instead of “happened” in every sentence?
Not always. The words overlap in meaning, but “occurred” can sound more formal, and “occur” has additional meanings involving being found or coming to mind. Choose the word that best fits the sentence and tone.
Conclusion: Occurred or Occured?
When choosing between “occurred or occured,” the correct answer is “occurred.”
“Occurred” is the standard past tense and past participle form of “occur.” It can mean that something happened, took place, was found in a particular place, or came to mind. Major dictionaries including Merriam-Webster and Cambridge identify “occurred” as the correct grammatical form.
The biggest spelling lesson is to remember the double letters.
“Occurred” contains two c’s and two r’s:
o-c-c-u-r-r-e-d
The common spelling “occured” contains only one r after the u, so it is incorrect.
Other variants such as “ocurred,” “ocurd,” “occurd,” “occurrd,” “occurredd,” “occurrred,” “occuried,” and “ocurrred” are also incorrect spellings.
If you are writing for a U.S. audience, the safest choice is always:
“occurred”
For everyday conversation, “happened” may sometimes sound more natural. For academic, business, technical, historical, and professional writing, “occurred” is a clear and useful word.
The easiest memory trick is simple:
“Occurred has two C’s and two R’s.”
Once you remember that pattern, the difference between “occurred or occured” becomes much easier to recognize.
