Overpayment relief is the statutory mechanism under the Taxes Management Act 1970 that allows a taxpayer to reclaim tax they have overpaid, including CIS deductions, when the normal amendment window for a Self Assessment return has closed.
The time limit is four years from the end of the relevant tax year. Because tax years end on 5 April, the four-year window runs from 5 April in the year the overpayment occurred. For example, overpayments in 2021/22 (which ended 5 April 2022) can be reclaimed until 5 April 2026. The deadline is not linked to 31 January (the Self Assessment filing deadline) and is not extendable.
This matters for CIS subcontractors in two situations:
- No return was ever filed for a year in which CIS deductions were taken. A late return can still be submitted to recover the overpaid deductions, provided the four-year window has not closed.
- A return was filed but expenses were missed or income was reported incorrectly. An amendment can be made, but once more than 12 months have passed since the filing deadline, the overpayment relief route (rather than a standard amendment) is the correct mechanism.
To make a claim, a subcontractor (or their agent) submits a letter or the online form to HMRC setting out the year, the amount of overpaid tax, and the supporting calculations. You will need CIS payment and deduction statements for each year, as HMRC will not accept a claim without evidence of the deductions taken.
HMRC processes overpayment relief claims separately from online Self Assessment repayments, so timelines vary. Claims covering multiple back years are handled year by year.
Our guide to CIS back-years refund claims covers the four-year rule in detail, including what records you need and a worked example of a multi-year claim.