Self Assessment UK: Registration, Filing, Payments on Account and PenaltiesOverpaid Tax Calculator UK — Check If HMRC Owes You a Refund
Find out if you've overpaid tax and how to claim it back from HMRC. Check P800 refunds, emergency tax, pension tax relief, and other common overpayments.
HMRC holds over £300 million in unclaimed tax refunds. Here’s how to check if you’ve overpaid and claim your money back.
Common Reasons for Tax Overpayment
| Reason | Typical Refund |
|---|
| Wrong tax code | £100 - £1,000+ |
| Emergency tax on new job | £200 - £2,000+ |
| Working only part of the year | £100 - £500 |
| Pension tax relief (higher-rate taxpayers) | £100 - £2,000+/year |
| Marriage Allowance not claimed | £252/year (up to 5 years = £1,260) |
| Working from home allowance | £62/year (up to £310 for 5 years) |
| Professional subscriptions | £20 - £200/year |
| Uniform/tools allowance | £60 - £140/year |
| Multiple jobs with incorrect codes | £200 - £1,500+ |
Quick Check: Are You Owed a Refund?
Answer these questions:
| Question | If Yes, Possible Refund |
|---|
| Did you start a new job this year without giving your P45? | Emergency tax — likely owed refund |
| Did you work for only part of the tax year? | May not have used full Personal Allowance |
| Are you a higher-rate taxpayer with a pension? | With a relief at source pension, the extra relief has to be claimed |
| Did you work from home during COVID or since? | Working from home allowance |
| Are you married with one low earner? | Marriage Allowance |
| Do you pay for work-related subscriptions? | Professional subscriptions relief |
| Do you wash or buy your own uniform? | Uniform/flat rate expenses |
Scenario 1: Emergency Tax (Wrong Tax Code)
How Emergency Tax Works
When an employer doesn’t have your tax information (no P45), they use an emergency tax code. This often results in overpayment.
| Emergency Code | What It Means | Likely Outcome |
|---|
| 1257L W1/M1 | Non-cumulative — each month treated separately | May overpay if early in year |
| BR | All earnings taxed at 20% | Overpay if below £12,570 annual earnings |
| 0T | No Personal Allowance given | Significant overpayment likely |
| D0 | All earnings taxed at 40% | Large overpayment likely |
Calculate Your Emergency Tax Overpayment
If you were on BR (all at 20%) when you should have had 1257L:
| Monthly Gross Pay | Tax Paid (BR) | Tax Owed (1257L) | Monthly Overpayment |
|---|
| £2,000 | £400 | £190 | £210 |
| £2,500 | £500 | £290 | £210 |
| £3,000 | £600 | £390 | £210 |
| £3,500 | £700 | £490 | £210 |
The overpayment is roughly £210 per month for average earners on BR instead of 1257L.
How to Fix
- Give your employer your P45
- If no P45, complete a starter checklist (form available from HMRC)
- Call HMRC on 0300 200 3300 to update your code
- Overpayment should be refunded through your wages once corrected
Scenario 2: Pension Tax Relief
Higher and additional rate taxpayers contribute to pensions from taxed income but with a relief at source pension only basic rate relief is added automatically. The extra relief must be claimed.
Unclaimed Pension Relief Calculator
| Your Annual Pension Contribution | Basic Rate Relief (automatic) | Higher Rate Relief (must claim) | Additional Rate Relief (must claim) |
|---|
| £5,000 | £1,250 | £1,250 | £1,562.50 |
| £10,000 | £2,500 | £2,500 | £3,125 |
| £20,000 | £5,000 | £5,000 | £6,250 |
| £40,000 | £10,000 | £10,000 | £12,500 |
How it works:
- You contribute £5,000 from post-tax income
- Basic rate relief of £1,250 is added automatically (£6,250 goes into pension)
- If you’re a 40% taxpayer and all £6,250 is in income taxed at 40%, you can claim an extra 20% of £6,250 (£1,250); at 45% the extra is 25% of the gross amount (£1,562.50)
How to Claim
| Tax Situation | How to Claim |
|---|
| Self-Assessment filer | Include on your tax return |
| Not filing Self-Assessment | Use HMRC’s online pension tax relief claim service, or write to HMRC if you cannot claim online |
| Multiple years unclaimed | Contact HMRC — can go back 4 years |
Scenario 3: Working From Home
Tax Relief for Home Workers
| Eligibility | Relief Available |
|---|
| Employer required you to work from home | £6/week flat rate (no receipts) |
| COVID home working (2020-2022) | Could claim for whole year |
| Regular home workers | Claim for days worked at home |
Calculate Your Refund
| Tax Rate | £6/week × 52 weeks | Tax Relief |
|---|
| Basic (20%) | £312 | £62.40 |
| Higher (40%) | £312 | £124.80 |
| Additional (45%) | £312 | £140.40 |
For COVID years (2020/21 and 2021/22), you could claim the full year even if you only worked from home for part of it.
How to Claim
- Go to gov.uk/tax-relief-for-employees/working-at-home
- Complete the online claim
- HMRC adjusts your tax code
- Refund comes through increased wages or direct payment
Scenario 4: Marriage Allowance
Unclaimed Marriage Allowance Refund
| Years Unclaimed | Potential Refund |
|---|
| Current year only | £252 |
| 2 years | £504 |
| 3 years | £756 |
| 4 years | £1,008 |
| 5 years | £1,260 |
Eligibility: One partner earns under £12,570, the other is a basic-rate taxpayer (under £50,270).
See our Marriage Allowance Calculator for details.
Scenario 5: Part-Year Working
If you only worked for part of the tax year (April 6 to April 5), you may not have used your full Personal Allowance.
Example: 6 Months of Work
| Item | Amount |
|---|
| Earned (6 months at £2,500/month) | £15,000 |
| Personal Allowance | £12,570 |
| Taxable income | £2,430 |
| Tax owed (20%) | £486 |
| Tax paid (cumulative) | £486 |
But if you left mid-year after paying tax monthly:
| Tax Actually Paid | Tax Owed | Refund |
|---|
| £1,000 | £486 | £514 |
When This Happens
| Situation | Action |
|---|
| Made redundant mid-year | May be due refund |
| Started work mid-year | May have unused allowance |
| Career break | Refund likely |
| Returned from abroad | Check tax position |
Flat-Rate Expense Allowances
| Industry | Annual Allowance | Tax Refund (20%) | Tax Refund (40%) |
|---|
| Healthcare (nurses, midwives) | £125 | £25 | £50 |
| Cabin crew | £720 | £144 | £288 |
| Uniformed police | £140 | £28 | £56 |
| Ambulance staff | £185 | £37 | £74 |
| Engineers | £140 | £28 | £56 |
| Builders | £140 | £28 | £56 |
How to Check Your Entitlement
- Go to gov.uk/tax-relief-for-employees/uniforms-work-clothing-and-tools
- Check the list of flat-rate expenses by industry
- Claim online or via Self-Assessment
Scenario 7: Professional Subscriptions
If you pay professional subscriptions or union fees, you may be able to claim tax relief.
| Type | Examples | Tax Relief |
|---|
| Professional body | ACCA, CIMA, CIPD, NMC, GMC | 20-45% of cost |
| Trade union | Unite, Unison, GMB | 20-45% of cost |
| Learned society | Law Society, Royal Colleges | 20-45% of cost |
Example
| Subscription | Cost | Tax Refund (20%) | Tax Refund (40%) |
|---|
| NMC registration | £120 | £24 | £48 |
| Trade union | £200 | £40 | £80 |
| Professional body | £350 | £70 | £140 |
HMRC maintains a list of approved bodies: gov.uk/government/publications/professional-bodies-approved-for-tax-relief-list-3
How to Check Your Tax Record
Step 1: Access Personal Tax Account
- Go to gov.uk/personal-tax-account
- Sign in with Government Gateway
- View your tax code history
- Check for P800 (tax calculation)
Step 2: Review Your P60
Your P60 (issued by April after tax year) shows:
| Section | What to Check |
|---|
| Total pay | Matches your payslips |
| Tax deducted | Seems reasonable for your income |
| NI contributions | Recorded correctly |
| Tax code | The code used matches your expected allowances |
Step 3: Calculate What You Should Have Paid
| Your Gross Annual Pay | Tax-Free Allowance | Taxable | Tax Owed (basic rate) |
|---|
| £25,000 | £12,570 | £12,430 | £2,486 |
| £30,000 | £12,570 | £17,430 | £3,486 |
| £35,000 | £12,570 | £22,430 | £4,486 |
| £40,000 | £12,570 | £27,430 | £5,486 |
Compare this to your P60 “tax deducted” figure.
Claiming Your Refund
If HMRC Has Identified the Overpayment (P800)
| Method | Time to Refund |
|---|
| Claim online | 5 working days |
| Wait for cheque | 60 days |
If You’ve Identified the Overpayment
| Situation | How to Claim |
|---|
| Emergency tax | Contact HMRC or wait for automatic correction |
| Pension tax relief | Self-Assessment or HMRC’s online claim service |
| Marriage Allowance | Apply at gov.uk/marriage-allowance |
| Expenses relief | P87 form or Self-Assessment |
| General overpayment | Contact HMRC on 0300 200 3300 |
Maximum Lookback Periods
| Type of Claim | How Far Back | Example (claiming in 2025/26) |
|---|
| PAYE overpayment | 4 years | Back to 2021/22 |
| Self-Assessment | 4 years | Back to 2021/22 |
| Marriage Allowance | 4 years | Back to 2021/22 |
| Pension tax relief | 4 years | Back to 2021/22 |
| Working from home | 4 years | Back to 2021/22 |