There are two different time limits and they are often confused. Twelve months to change a return you already filed; four years to claim back tax you overpaid. Which one you need depends on whether a return exists.
Three situations
File it. The deductions are set against the liability for that year and the excess is repaid in the ordinary way. Late filing penalties may apply to the return itself, and they apply whether or not tax was owed — so a year in which you were due a refund can still carry a penalty for not having filed. Filing is still worth doing.
You have twelve months from the Self Assessment filing deadline to amend a return. For the tax year ending 5 April 2025, the filing deadline was 31 January 2026, so the return can be amended until 31 January 2027.
You claim overpayment relief instead. This must be made in writing to HMRC and can be claimed up to four years after the end of the tax year it relates to. It has to state the tax year, the amount you believe was overpaid, why, and that you are claiming overpayment relief.
The tax year ending 5 April 2023 ends on 5 April 2023. A claim for overpayment relief for that year must reach HMRC by 5 April 2027. After that the year is closed and the money cannot be recovered, however clear the case.
Both limits run from fixed dates that do not move. If you have several years outstanding, deal with the oldest first, because it expires soonest.
Contractors are required to keep CIS records for at least three years after the end of the tax year they relate to, so a request for a duplicate statement is more likely to succeed for a recent year than an old one.
Refund firms usually charge a percentage of what they recover, and some take a deed of assignment so HMRC pays them and they pass on the balance. That is legal, but it means the refund is not paid to you and the arrangement can cover future years as well. Read what you are signing, check whether the fee is a percentage or a fixed amount, and check whether it covers the tax return itself or only the claim. HMRC publishes guidance on this at gov.uk.
Four. A claim for overpayment relief can be made up to four years after the end of the tax year it relates to, so a claim for the year ending 5 April 2023 must reach HMRC by 5 April 2027. If the return for a year was never filed at all, filing it is the route rather than a relief claim, and if you filed within the last twelve months you amend the return instead.
Yes. The right to a repayment attaches to the tax year in which the deductions were taken, not to what you are doing now. Someone who left the trade partway through a year is often owed the most, because deductions were taken on a run rate that assumed a full year of income. The same four-year limit applies.
Ask for them first — a contractor must issue a payment and deduction statement for each payment period within 14 days of the end of that period, and must keep CIS records for at least three years after the end of the tax year. If they will not or cannot, HMRC holds the returns the contractor filed against your UTR and can confirm what was reported. Where a deduction was taken but never reported, that is a matter to raise with HMRC directly, with whatever evidence you have of the payment.
Late filing penalties apply to the return, and they apply whether or not there is tax to pay — so a year in which you were owed a repayment can still attract one. That is not a reason to leave it unfiled, because the penalty does not grow smaller and the repayment expires. Where there is a reasonable excuse, penalties can be appealed.
We will work out which years are still open, which are closest to expiring, and what each one is likely to be worth before you commit to anything.