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? | Pension tax relief likely unclaimed |
| 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 only get basic rate relief 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 | £1,000 | £1,250 |
| £10,000 | £2,500 | £2,000 | £2,500 |
| £20,000 | £5,000 | £4,000 | £5,000 |
| £40,000 | £10,000 | £8,000 | £10,000 |
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, you can claim an additional £1,000 back
- If 45% taxpayer, claim £1,250 back
How to Claim
| Tax Situation | How to Claim |
|---|
| Self-Assessment filer | Include on your tax return |
| Not filing Self-Assessment | Call HMRC or complete P87 form |
| 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 call HMRC |
| 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 |