their's (theirs)

'Their's' is a common misspelling. The correct form is 'theirs' - a possessive pronoun that never takes an apostrophe.

Below: a short rule, focused examples for work, school and casual use, copyable rewrites, and memory tricks to help you fix sentences quickly.

Quick answer

'Theirs' is correct. 'Their's' is wrong. Possessive pronouns (mine, yours, his, hers, ours, theirs) never use an apostrophe.

'Their' + noun = determiner before a noun (their report).
'Theirs' = standalone possessive (The report is theirs).
Don't confuse with contractions: they're = they are; there = place.

Core explanation: what 'theirs' does

'Theirs' replaces a noun phrase to show ownership: "The red folder is theirs." Apostrophes mark contractions (it's = it is) or possessive nouns (the manager's desk), not possessive pronouns.

Rule: possessive pronouns (mine, yours, his, hers, ours, theirs) → no apostrophe.
If you see "their's", it's a spelling error, not an alternate form.

Quick reference - grammar you can check fast

Decide whether you need a determiner + noun (their) or a standalone pronoun (theirs).

Before a noun: use their (their laptop).
Alone as owner: use theirs (The laptop is theirs).
Contraction? they're = they are. Location? there.

Right: Their proposal (determiner + noun).
Right: The proposal is theirs (standalone possessive).
Wrong: Their's proposal (incorrect).

Spacing, apostrophes and hyphenation: common punctuation traps

Adding an apostrophe or inserting a space with 's' after a pronoun is almost always wrong: their's, their 's, her's, our's.

Wrong spacing: their 's or their's - both incorrect.
Hyphen vs apostrophe: a hyphen links words (well-known); an apostrophe marks contractions or noun possession.
If you mean they are, write they're. If you mean ownership, write their or theirs as needed.

Wrong: Their's turn came first.
Right: Their turn came first.

Real usage: short, concrete examples for work, school and casual

Real sentences you might write - each shows the correct form and a common incorrect variant.

Work:
Wrong: Their's team submitted the draft late. →
Right: Their team submitted the draft late.
Work:
Wrong: The final deliverable was their's. →
Right: The final deliverable was theirs.
Work:
Right: The slides are theirs to update before Monday.
School:
Wrong: That chapter is their's responsibility. →
Right: That chapter is their responsibility.
School:
Right: The notebook on the desk is theirs.
School:
Wrong: Who left their's essay on the table? →
Right: Who left their essay on the table?
Casual:
Wrong: Is that jacket their's? →
Right: Is that jacket theirs?
Casual:
Right: Those seats are theirs - let's sit over there.
Casual:
Wrong: Their's umbrella is by the door. →
Right: Their umbrella is by the door.

Common wrong/right pairs you can copy (practice set)

Copy these pairs into your notes and practice replacing the wrong sentence with the right one until it feels automatic.

Pair: Wrong: Their's is the red suitcase by the gate. →
Right: Theirs is the red suitcase by the gate.
Pair: Wrong: Is that coat their's? →
Right: Is that coat theirs?
Pair: Wrong: The prize is their's to claim. →
Right: The prize is theirs to claim.
Pair: Wrong: Their's were the only comments that mattered. →
Right: Theirs were the only comments that mattered.
Pair: Wrong: We fixed their's error on the spreadsheet. →
Right: We fixed their error on the spreadsheet.
Pair: Wrong: Their's was the last word at the meeting. →
Right: Theirs was the last word at the meeting.
Pair: Wrong: Their's idea won the prize. →
Right: Their idea won the prize. (Or: The idea was theirs.)
Pair: Wrong: That choice is their's alone. →
Right: That choice is theirs alone.
Pair: Wrong: Their's notes were scattered across the desk. →
Right: Their notes were scattered across the desk.
Pair: Wrong: Their's phone kept ringing. →
Right: Their phone kept ringing.
Pair: Wrong: The responsibility is their's. →
Right: The responsibility is theirs.
Pair: Wrong: Who left their's bag here? →
Right: Who left their bag here? (Or: Whose bag is this?)

Try your own sentence

Test the whole sentence, not just the single word. Context usually makes the correct choice obvious.

Rewrite help: copyable fixes and quick checklist

Checklist: 1) Is the word before a noun? → use their + noun. 2) Is it standing alone as ownership? → use theirs. 3) Did you mean they are? → use they're.

If you can replace the phrase with "belong(s) to them", use theirs. (The files belong to them → The files are theirs.)
Fallback rewrite: "X belongs to them" works in both formal and casual writing.

Rewrite:
Work:
Wrong: "Their's presentation was incomplete." →
Right: "Their presentation was incomplete." Or: "The presentation was theirs."
Rewrite:
School:
Wrong: "That section is their's to summarize." →
Right: "That section is theirs to summarize."
Rewrite:
Casual:
Wrong: "Is that seat their's?" →
Right: "Is that seat theirs?" Or: "Whose seat is that?"
Template A (before noun): replace "their's [noun]" → "their [noun]".
Template B (standalone): replace "their's" → "theirs" or "belongs to them".

Fix your own sentence: diagnostics, templates and three quick fixes

Diagnostic: Say the sentence aloud and substitute "belong(s) to them." If it still makes sense, use theirs. If the word sits before a noun, use their.

Drop-in template: "The [item] is theirs."
Before-noun template: "Their [noun] is [adjective]."

Fix: "Their's problem was the deadline." → "Their problem was the deadline." Or: "The problem belongs to them."
Fix: "Who left their's bag here?" → "Who left their bag here?" Or: "Whose bag is this?"
Fix: "That choice was their's alone." → "That choice was theirs alone."

Memory tricks and quick practice drills

Two fast tricks: group them with other possessive pronouns that never take apostrophes; treat any apostrophe after a pronoun as a red flag.

Say aloud: mine / yours / his / hers / ours / theirs - none have apostrophes.
Proofread drill: search for "their'" or "their's" and apply the checklist to each hit.
Daily drill: rewrite three sentences using their/theirs correctly.

Practice: Convert forms: "Their's turn next" → "Theirs is next" → "It's their turn next" (try all three).

Similar mistakes to watch for (fast fixes)

Writers often mix up their / they're / there and its / it's. Use the function test: possession (no apostrophe) vs contraction (apostrophe) vs place.

they're = they are; there = location; their = determiner before a noun.
it's = it is; its = possessive pronoun (no apostrophe).
Never add apostrophes to possessive pronouns: hers, ours, yours, theirs, his, mine.

Pair: Wrong: Their going to bring dessert tonight. →
Right: They're going to bring dessert tonight.
Pair: Wrong: Its a good idea to check their's first. →
Right: It's a good idea to check theirs first.
Pair: Wrong: Her's was the best answer. →
Right: Hers was the best answer.

FAQ

Is 'their's' ever correct?

No. 'Their's' is not correct in standard English. Use 'their' before a noun and 'theirs' as a standalone possessive pronoun.

How do I choose 'their' vs 'theirs'?

'Their' goes before a noun (their homework). 'Theirs' stands alone and replaces the noun phrase (The homework is theirs).

Do possessive pronouns ever use apostrophes?

No. Possessive pronouns (mine, yours, his, hers, ours, theirs) do not take apostrophes. Apostrophes appear in contractions and in noun possession.

What quick check catches most errors?

Substitute "belong(s) to them" into the sentence. If it still makes sense, use 'theirs'. If not and the word precedes a noun, use 'their'.

How can I fix many instances at once?

Search your document for "their'" or "their's" and apply the three-step checklist: determine function → pick their/theirs → rewrite. A focused search-and-replace will catch most repeats.

Quick tip before you send that message

If you spot "their's", choose one short fix (their + noun, theirs, or rewrite as "belongs to them") and paste it in. A one-line search-and-replace across your draft will remove most errors.

If you want a second opinion, paste the sentence into a grammar tool for an instant correction and brief explanation.