The short answer
Longer than most people assume, and not forever. An unpaid invoice stays legally collectable for a period set by where you are, commonly several years, after which a court will refuse to hear the claim however clearly the money is owed.
Find the period that applies to you, because it varies by country and by state.
Know when the clock started, which is usually when payment fell due.
Understand what can restart it, since a part payment or a written acknowledgement may.
Keep the evidence while the period runs, not only while you are actively pursuing it.
Treat the legal deadline and your own write-off decision as 2 different things.
The practical consequence surprises people in both directions. An invoice you gave up on 2 years ago may still be enforceable, and an invoice you have been patiently reminding somebody about for years may be closer to expiry than you think.
What a limitation period does
It bars the claim rather than cancelling the debt. Cornell's definition of a statute of limitations describes a law that bars claims once a set period has passed, with the clock typically running from the date of the injury, the date it was discovered, or the date it would have been discovered with reasonable effort. Once it expires, the claim can no longer be pursued.
So the money remains owed in principle. The client can still choose to pay it, and you can still ask. What you lose is the ability to make a court compel them, which is the thing that gives every other step its weight.
That matters for the realistic routes too. A collections agency will rarely take a claim close to expiry, and a demand letter carries considerably less implication when the deadline behind it has passed.
How long, roughly
There is no single answer, and anyone offering one is describing their own jurisdiction.
Where | Position | Note |
|---|---|---|
US | Set by each state | Commonly a few years, and often longer for written contracts than oral ones |
EU | National law | No harmonised period for contract debts |
UK | 6 years for simple contract | From the date the cause of action accrued |
In the US the period is a matter of state law and differs both between states and between types of claim, with written contracts typically given longer than oral ones. Your own state court's published information is the authority, and it is the same place to look as for small claims limits, which also vary considerably.
In England and Wales the position is statutory and simple. Section 5 of the Limitation Act 1980 provides that an action founded on simple contract shall not be brought after the expiration of 6 years from the date the cause of action accrued. An unpaid invoice is an ordinary contract claim, so 6 years from when payment fell due is the working assumption.
In the EU, limitation is national rather than harmonised, so a German client, a Spanish one and a Dutch one may each sit behind a different deadline. Where the contract names a governing law, that is the place to start.
When the clock starts
Usually when payment became due rather than when you delivered the work or raised the invoice. On net 30, an invoice dated 1 March typically starts its clock on 31 March.
That distinction rarely matters at the start and matters enormously at the end, because the difference between those 2 dates can be the difference between a claim and a regret. Record the due date rather than only the invoice date, which is also what makes the ageing report in the weekly review meaningful.
What can restart it
This is the part most people do not know, and it can work strongly in your favour.
In England and Wales, section 29 of the Limitation Act provides that where a person liable for a debt acknowledges the claim or makes a payment in respect of it, the right of action is treated as having accrued on the date of that acknowledgement or payment. In plain terms, a client who writes that they know they owe you, or who pays part of the balance, may restart the whole period.
Similar principles exist in many US states, though the requirements differ and some demand a signed writing. The direction is consistent enough to be worth knowing: an email from a client accepting that the invoice is owed is a more valuable document than it looks, and a part payment accepted today may extend your position by years.
Which gives a practical habit. When a client acknowledges a debt in writing, keep that message somewhere you will find it, filed with the invoice. It is the cheapest insurance in this article.
The legal deadline and your own decision
These are separate, and conflating them causes 2 different mistakes.
The first is treating the limitation period as a reason to keep pursuing something. An invoice can be enforceable for years and still be a poor use of your attention, which is the arithmetic in when to write off an unpaid invoice. Writing it off in your books does not shorten the legal period, and you can still accept payment later.
The second is assuming that because you wrote it off, it is gone. An old invoice from a client who later becomes solvent, or who reappears wanting to work with you again, is a real asset and often a quietly effective thing to raise.
The rule of thumb: decide commercially on the economics, and let the legal deadline govern only the question of whether a court route remains available.
Keeping the evidence alive
A claim is worth what you can prove, and the records that support it are the ones most likely to be lost in a laptop change 3 years later. While the period runs, keep:
The contract or accepted proposal, and anything amending it.
The invoice, and evidence it was delivered and received.
Proof the work was delivered and, ideally, accepted.
Every written acknowledgement of the debt or promise to pay.
The log of contact: dates, names and what was said.
Store it with the client record rather than in a mailbox, for the same reason that a shared billing address beats a personal inbox. The evidence usually outlives the person who gathered it.
FAQ
How long do I have to collect an unpaid invoice?
It depends where you are. In England and Wales it is 6 years for a simple contract claim from when the cause of action accrued. In the US it is set by each state and varies by claim type. In the EU it is national law, with no harmonised period.
When does the time limit start?
Usually when payment fell due rather than when you delivered the work or issued the invoice. On net 30 terms, an invoice dated 1 March generally starts its clock on 31 March.
Can the time limit be restarted?
Often, yes. Under English law an acknowledgement of the debt or a payment in respect of it treats the right of action as accruing from that date. Similar principles exist in many US states, sometimes requiring a signed writing. Keep any written acknowledgement.
Does writing off an invoice affect the time limit?
No. A write-off is an accounting decision recording that you do not expect the money. The legal period is unchanged, the debt survives, and a later payment is recorded as income when received.
Can I still ask for payment after the period expires?
You can ask, and a client may still choose to pay. What you lose is the ability to have a court compel them, which also weakens a demand letter and makes a collections agency unlikely to take it on.
What should I keep, and for how long?
The contract, the invoice, evidence of delivery and acceptance, any written acknowledgement of the debt and your contact log, kept with the client record for at least as long as the period runs where you are.
Not legal advice. Limitation periods, when they start and what restarts them vary by state and by country and turn on the specific facts. Take advice before relying on or abandoning a claim.