Millions of UK taxpayers are owed money by HMRC each year without realising it. Overpayments happen more often than you would think — especially around job changes, incorrect tax codes, and unclaimed reliefs. This guide explains the most common refund scenarios and how to get your money back.
Common reasons for a tax refund
- Emergency tax code: you overpaid tax when starting a new job because HMRC had not issued the correct code yet
- Job change mid-year: your employer assumed you would earn more than you actually did in the remaining months
- Leaving a job and not working for part of the year: you may not have used your full Personal Allowance
- Unclaimed work expenses: uniform washing, tools, professional subscriptions you have not claimed relief on
- Pension contributions not reflected: higher-rate relief not claimed through Self-Assessment
- Marriage Allowance not claimed: up to 4 years of backdated claims available
- CIS overpayment: construction workers whose 20% deductions exceed actual tax owed
How to check if you are owed a refund
Option 1: HMRC Personal Tax Account. Log in at GOV.UK and check your tax summary for each year. HMRC will show if you have overpaid and may already have issued a P800 calculation.
Option 2: Compare your P60 to the calculator. Enter your total salary into the income tax calculator and compare the expected annual tax to what your P60 shows was deducted. A significant difference suggests overpayment.
How to claim your refund
- P800 / Simple Assessment: HMRC sends these automatically after the tax year ends. If it shows you are owed money, you can claim online and receive it within 5 days.
- Self-Assessment: if you file a return, any overpayment is refunded automatically (or offset against future payments on account).
- Form P87: for employment expense claims under £2,500 (no Self-Assessment needed).
- Write to HMRC: for cases not covered above, write to your tax office with supporting documents.
How far back can you claim?
You can claim a refund for the current tax year plus the previous 4 tax years. For 2026/27, that means you can go back to 2022/23. Beyond 4 years, HMRC will generally not refund overpayments.
Verify your expected tax
The quickest way to spot an overpayment is to compare what youshould have paid with what was actually deducted. The income tax calculator gives you the "should have paid" figure in seconds.