Reclaiming Overpaid Tax from HMRC — A Trade Business Guide (2026)

The Common Ways Trades Overpay HMRC

Overpayment is rarely deliberate. It tends to come from the way tax is collected — particularly the system of paying in advance — rather than from a mistake on your part. The four most common causes for trades are below.

Payments on Account Set Too High

If your Self Assessment tax bill is more than £1,000 and less than 80% of your tax was collected at source, HMRC asks you to make payments on account — two advance instalments toward next year's bill, each equal to half of this year's liability, due on 31 January and 31 July. The system assumes next year will look like last year.

For a trade, that assumption breaks easily. A roofer who had a bumper year and then loses a big contract, or a sole trader who scales back hours, can end up paying instalments calculated on income they will never earn. The result is that you hand HMRC money against a tax bill that turns out to be far smaller. That gap is an overpayment waiting to be reclaimed — or, better, reduced before it ever leaves your account.

CIS Deductions Exceeding Your Actual Bill

Subcontractors in the Construction Industry Scheme have tax deducted at source on every payment from a contractor — 20% if you are registered, 30% if you are not. Those deductions are an advance payment of your Income Tax and Class 4 National Insurance.

The problem is that 20% is deducted from your labour total with no account taken of your expenses, your tax-free Personal Allowance, or your tax bands. A subcontractor with significant van, fuel, tool and materials costs will almost always have had more deducted across the year than they actually owe. When the return is filed and the real liability is worked out, the excess CIS tax becomes a refund. Many CIS subcontractors are owed a refund every single year.

Emergency Tax on a Previous Job

If you left employment to go self-employed — or did some PAYE work alongside your trade — you may have been put on an emergency or wrong tax code at some point. Emergency codes often ignore part of your Personal Allowance, so too much tax is taken from your wage. If that overpayment was never corrected through PAYE, it can usually be recovered, either through your Self Assessment return or by claiming directly for the relevant year.

Expenses You Never Claimed

This is the quiet one. Every allowable cost you fail to put on your return inflates your taxable profit, which inflates your bill, which means you overpay. Mileage, use of home as office, tools and small equipment, protective clothing, public liability insurance, accountancy fees, phone and software subscriptions — trades routinely leave hundreds or thousands of pounds of legitimate deductions off the return. If you spot missed expenses on a return you have already filed, you can usually amend it (see the time limits below) and recover the difference.

How a Self Assessment Refund Is Triggered

For most trades, the refund mechanism is simply the Self Assessment return itself. When you file, HMRC compares what you actually owe for the year against what has already been paid toward it — your payments on account, plus any CIS tax deducted at source, plus any tax already taken under PAYE.

If the total paid exceeds the total owed, your online account shows the difference as an overpayment sitting in your favour. There is no special form to fill in to create the refund — filing an accurate return is what surfaces it. The two things that make the biggest difference to whether a refund appears are filing on time and making sure every allowable expense and every CIS deduction is entered correctly. If you under-record your CIS deductions, you will be refunded less than you are owed.

Claiming to Reduce Your Payments on Account

Getting a refund is fine, but it is money HMRC has held for months that could have been in your business. The better move, if you can see a quieter year coming, is to claim to reduce your payments on account so you never overpay in the first place.

You can apply to reduce them through your HMRC online account (or on form SA303, or by asking your accountant) when you reasonably expect your income — and therefore your tax bill — to be lower than the previous year. This is common after losing a major client, scaling back, taking time off through illness, or any structural drop in turnover.

One important warning: only reduce if you genuinely expect lower profits. If you cut your payments on account too far and your actual bill comes in higher, HMRC charges interest on the shortfall from the original due dates. Base the reduction on a realistic forecast, not wishful thinking — and keep a note of how you arrived at the figure.

The Four-Year Time Limit for Overpayment Relief

What if the overpayment is on an earlier year — one you can no longer amend in the normal way? This is where overpayment relief comes in. It is the route for reclaiming tax you paid but did not actually owe on a year that is now closed to ordinary amendment.

The key rule is the deadline: an overpayment relief claim must reach HMRC within four years of the end of the tax year the overpayment relates to. So for the 2021/22 tax year (which ended on 5 April 2022), the claim must be made by 5 April 2026. Miss the four-year window and the right to reclaim is normally lost, however clearly you overpaid.

A claim must be made in writing, must state that it is a claim for overpayment relief, must quantify the amount you believe was overpaid, and must include the grounds and supporting evidence. Because the bar for a valid claim is specific, older-year overpayment claims are an area where it is worth getting an accountant to draft the letter.

How HMRC Pays Your Refund

Once an overpayment is confirmed, you generally have two outcomes:

• Bank transfer: If you add your account details to your HMRC online account and request repayment, the refund is paid directly to your bank — usually the quickest method. CIS refunds for sole traders are commonly paid this way after the return is processed.
• Set against your next bill: HMRC may automatically offset an overpayment against tax you are due to pay — for example crediting it toward your next payment on account rather than refunding cash. If you would rather have the money back, request the repayment explicitly rather than leaving it to be carried forward.

Timescales vary. A straightforward Self Assessment repayment requested online can arrive within a couple of weeks, but HMRC runs security checks on some claims, and refunds involving CIS or older years can take longer. Limited company refunds (for example overpaid Corporation Tax) follow a separate process and are repaid to the company, not to you personally.

Check Your HMRC Online Account

Your HMRC online account (or the HMRC app) is the first place to look. It shows your Self Assessment statement, any overpayment currently sitting in your favour, your payments on account schedule, and the running balance of what you owe or are owed. For CIS subcontractors, it is where you confirm the deductions recorded against you match your own records.

Check it before each payment-on-account deadline and again after you file. If the figures do not match your own bookkeeping — particularly your CIS deductions — that mismatch is exactly what causes refunds to be missed or underpaid. Keeping your job and payment records clean throughout the year, so you can reconcile against HMRC's figures, is the single best protection against quietly overpaying.

Beware of Refund Scam Texts and Emails

Tax refunds are one of the most heavily exploited scams aimed at the self-employed. The rule is simple: HMRC will never text or email you a link to claim a refund, and will never ask for your bank or card details by text, email or social media message.

A message saying "You are owed a tax rebate of £XXX, click here to claim" is a phishing attempt, no matter how official it looks. So is any call demanding your details to "release" a refund. Genuine refunds appear in your HMRC online account and are paid to the bank details you have entered there yourself. If in doubt, do not click anything — log in to your HMRC account directly through GOV.UK, and forward suspicious texts to 60599 and emails to phishing@hmrc.gov.uk.

When to Involve an Accountant

Plenty of straightforward refunds — a typical CIS subcontractor overpayment, or an overpayment shown on a filed return — you can handle yourself through your HMRC online account. But an accountant earns their fee in a few situations:

• Overpayment relief on older years: The written claim has strict content requirements and a hard four-year deadline. A poorly drafted claim can be rejected.
• Deciding how far to reduce payments on account: Getting the forecast wrong triggers interest. An accountant can model it against your actual figures.
• Mixed PAYE and self-employment, or wrong tax codes: Untangling overpayments across employment and trade can be fiddly.
• Limited company refunds: Corporation Tax overpayments and director overpayments interact, and the routes differ from sole trader Self Assessment.
• Larger sums or HMRC queries: If a refund is significant or HMRC opens an enquiry, professional representation pays for itself.

Quick Reference: Reclaiming Overpaid Tax (2026)

Time limits are the thing to watch. The four-year overpayment relief window in particular is unforgiving — if you suspect you overpaid on an older year, act well before the deadline rather than leaving it.