Formally means in a formal way — officially, or according to convention: "He was formally introduced to the board." Formerly means previously, at an earlier time: "The building, formerly a bank, is now a café." One is about manner, the other about time.
The core difference
Formally is the adverb of formal. Formerly is the adverb of former. The words look like near-twins because a single vowel separates them, and in quick speech they sound nearly identical — which is why the mistake survives every proofread and every spellchecker.
Using formally
- "The merger was formally announced on Tuesday."
- "Guests are asked to dress formally."
- "She has never been formally trained."
- "The complaint was formally withdrawn."
Note the two flavours: officially recognised ("formally announced") and stiffly or conventionally ("dress formally", "write formally"). Both come from the same root idea of following a set form.
Using formerly
- "X, formerly Twitter, changed its terms again."
- "He was formerly head of research at the institute."
- "The road, formerly a canal towpath, floods every winter."
Formerly always points backwards in time and always implies the situation has changed. If nothing has changed, use previously only where it fits or drop the word entirely.
The test
Substitute the plain synonyms. If officially or politely fits, you want formally. If previously or once fits, you want formerly. "He was previously head of research" works, so formerly is right. "He was officially head of research" says something quite different — which is a useful reminder that choosing the wrong one does not produce nonsense, it produces a sentence that is wrong but readable. That is exactly why it slips through.
The memory trick
Formerly contains er, as in earlier — both are about time. Formally contains al, as in a formal occasion. Or simply: former means the earlier of two, and formerly inherits that meaning unchanged.
The mistake you will see most
Company and rebrand announcements are the epicentre. "Meta, formally known as Facebook" appears constantly, and it is wrong every time — the correct phrase is formerly known as, which is where the abbreviation f/k/a in legal documents comes from. Job bios attract the same error: "formally of the Guardian" should be "formerly of the Guardian".
The reverse mistake is rarer but does occur: "the couple were formerly married in a registry office" should be formally, unless you really mean they used to be married.
One more relative
Keep formulaic and informally out of the mix. And note that formal has no time sense at all — there is no such thing as "a formal employer" meaning a previous one; that is a former employer.
Frequently Asked Questions
Is it 'formally known as' or 'formerly known as'?
"Formerly known as" — it means previously called. "Formally known as" would mean known by that name in official contexts, which is almost never what a rebrand announcement intends.
Which one do I use for a previous job title?
Formerly. "She was formerly chief executive of the trust." Formally would suggest her chief executive role was official rather than earlier, which makes no sense in a bio.
Do formally and formerly sound the same?
Close but not identical. Formally has three syllables with an -al- in the middle; formerly has an -er-. In fast connected speech they often collapse into the same sound, which is why the spelling error is so common.