once and (in) a while

Use once in a while (three words) to mean "occasionally." Avoid the non-standard slip once and a while, especially in writing and careful speech.

Quick answer

Write once in a while. Replace "and" with "in" whenever you mean "occasionally." Hyphenate only when the phrase modifies a noun (a once-in-a-while reminder).

Correct: once in a while = occasionally.
Incorrect: once and a while = non-standard; avoid in edited writing.
Hyphenate as a compound adjective before a noun: a once-in-a-while treat.

Core explanation

Once in a while places one occurrence inside a stretch of time: you do something once within a while. The preposition in is essential to that idiom.

'Once and a while' drops the required preposition; you may hear it in speech, but it reads as non-standard in writing.

Rule: once + in + a while = occasionally.
If you see 'and' between once and a while, change it to 'in'.

Grammar: why "in" matters

Prepositions are often fixed in idioms. Swapping them usually breaks the idiom or makes it non-standard. Here, in marks the time frame that contains the single occurrence.

Idioms freeze small words like prepositions; don't swap them.
If you prefer a single-word substitute in formal writing, use occasionally or periodically.

Contrast: Correct: She visits once in a while.
Incorrect: She visits once and a while.

Hyphenation: when to use once-in-a-while

Hyphenate only when the phrase acts as a single adjective before a noun. Do not hyphenate when it functions adverbially after a verb.

Use: a once-in-a-while reminder (hyphenated, adjective).
Don't use: I get reminders once in a while (no hyphens, adverbial).

Spacing and variants to avoid

The idiom requires "a while" as two words. Awhile (one word) means "for a short time" and does not follow "once in."

Correct: once in a while (three words).
Incorrect: once in awhile, onceinawhile, once and a while.

Awhile vs. a while: Wrong: I'll stay awhile once in a while.
Right: I'll stay for a while once in a while.

Real usage & tone

Once in a while suits neutral and conversational contexts. In formal reports or academic writing, prefer occasionally, periodically, or from time to time for a cleaner tone.

Use once in a while in emails, blog posts, and casual writing.
Use occasionally or from time to time in formal documents.

Formal vs casual: Formal: We audit accounts periodically.
Casual: We audit accounts once in a while.

Try your own sentence

Read the whole sentence to see if the idiom fits. Context usually makes the right wording clear.

Concrete examples: wrong → right (work, school, casual)

Below are paired sentences labeled WRONG and RIGHT. Use the RIGHT sentence as a direct replacement.

Work - Wrong: I'll send the weekly summary once and a while.
Work - Right: I'll send the weekly summary once in a while.
Work - Wrong: We review the backlog once and a while during sprint planning.
Work - Right: We review the backlog once in a while during sprint planning.
Work - Wrong: Please check the dashboard once and a while for new tickets.
Work - Right: Please check the dashboard once in a while for new tickets.
School - Wrong: Teachers ask students to revise essays once and a while.
School - Right: Teachers ask students to revise essays once in a while.
School - Wrong: I go to the library once and a while to work on projects.
School - Right: I go to the library once in a while to work on projects.
School - Wrong: Once and a while we schedule group study sessions.
School - Right: Once in a while we schedule group study sessions.
Casual - Wrong: I meet my friends for coffee once and a while.
Casual - Right: I meet my friends for coffee once in a while.
Casual - Wrong: Once and a while I binge a new TV show.
Casual - Right: Once in a while I binge a new TV show.
Casual - Wrong: We go out to dinner once and a while.
Casual - Right: We go out to dinner once in a while.

How to fix your sentence - quick rewrites

Checklist: find "once and a while" → change "and" to "in" → hyphenate if it precedes a noun → consider occasionally for formal tone.

Search for "once and a while" and replace with "once in a while."
If the phrase modifies a noun before it, hyphenate: once-in-a-while reminder.
In formal writing, use "occasionally" or "from time to time."

Rewrite:
Wrong: You're supposed to backup your work once and a while. →
Right: You're supposed to back up your work once in a while.
Rewrite:
Wrong: Once and a while, a typo slips into the report. →
Right: Once in a while, a typo slips into the report. (
Formal: Occasionally, typos appear in the report.)
Rewrite:
Wrong: I call my parents once and a while. →
Right: I call my parents once in a while.

Memory tricks and final tip

Two quick tricks: (1) Read the capitals: Once IN A While - the middle word is IN. (2) Visualize a time window: you do the action once inside a while (IN a while).

If you catch yourself saying "and," pause and swap it to "in," or use occasionally until the correct phrase feels automatic.

Mnemonic: Once IN A While → IN is the needed connector.
Habit: add a quick search/replace for "once and a while" → "once in a while."
Tip: Bind a snippet so typing "oiaw" expands to "once in a while" in messages.

Similar mistakes to watch for

People often swap prepositions or conjunctions in fixed idioms. Spotting one error helps you catch others.

Once and for all = a definitive action; it has a different meaning from once in a while.
Now and then / every now and then = correct; don't change their prepositions.
Awhile (one word) means "for a short time" and is not interchangeable with "a while" here.

Related: Correct: We meet every now and then.
Incorrect: We meet every in and then.

FAQ

Is "once and a while" acceptable in casual speech?

You may hear it in speech, but it's non-standard. For clear written communication and careful speech, use "once in a while" or "occasionally."

When should I hyphenate the phrase?

Hyphenate only when the phrase appears before a noun as a single adjective: "a once-in-a-while audit." Do not hyphenate when it's used adverbially after a verb.

Can I write "once in awhile" (one word)?

No. "Awhile" is an adverb meaning "for a short time." The idiom requires "a while" as two words: "once in a while."

What formal alternatives work in reports?

Use "occasionally," "periodically," or "from time to time" in formal writing for a cleaner tone.

How do I stop making this mistake?

Search your draft for "once and a while" and replace it with "once in a while" or "occasionally." Use the "Once IN A While" mnemonic and consider a text snippet to automate the correct phrase.

Quick action you can take now

Before sending an email or submitting a paper, search for "once and a while" and replace "and" with "in" - or substitute "occasionally" for a formal tone.

A simple search/replace or a text snippet prevents the error and keeps your writing cleaner.