Tax

Overpaid 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.

By PocketWise · · 6 min read

Tax information is based on HMRC rules for the 2026/27 tax year. Tax rules can change — always verify current rates at GOV.UK. This is not tax advice. Consider consulting a qualified tax adviser for your personal situation.

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

  1. Give your employer your P45
  2. If no P45, complete a starter checklist (form available from HMRC)
  3. Call HMRC on 0300 200 3300 to update your code
  4. 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

  1. Go to gov.uk/tax-relief-for-employees/working-at-home
  2. Complete the online claim
  3. HMRC adjusts your tax code
  4. 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

Scenario 6: Uniform and Work Expenses

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

  1. Go to gov.uk/tax-relief-for-employees/uniforms-work-clothing-and-tools
  2. Check the list of flat-rate expenses by industry
  3. 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

  1. Go to gov.uk/personal-tax-account
  2. Sign in with Government Gateway
  3. View your tax code history
  4. 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

Sources

  1. HMRC — Claim a tax refund