Understand Your Payslip, Tax Code and PAYE / Lesson 8 of 8
What to do when your code is wrong
Four years of overpaid tax is still claimable. Five is not.
The short answer
- ✓ Check the code number, its deductions, and the letter against your situation
- ✓ Corrections go through your Personal Tax Account and reach your employer quickly
- ✓ Overpayments can only be reclaimed for four tax years
- ✓ Not receiving a P800 does not mean your tax was right
How to tell whether it is wrong
Work through this in order. Most wrong codes fail at one of the first three.
- Does the number times ten match the allowance you should have?
- Are the deductions on your P2 still true today?
- If this is your only job, is the letter L rather than BR, D0 or 0T?
- If you live in Scotland or Wales, is there an S or C prefix?
- Are you still on W1, M1 or X after two pay periods?
Getting it changed
Use your Personal Tax Account on GOV.UK. You can see how your code was built, correct estimated figures, remove benefits you no longer receive, and add expenses you are entitled to. Changes usually flow through to your employer within a pay period or two.
Have to hand: your National Insurance number, your employer's PAYE reference from your payslip, and the figures you are correcting.
Getting overpaid tax back
| Situation | What happens |
|---|---|
| Overpaid earlier this tax year | Corrected through your code, usually next payslip |
| Overpaid in a previous tax year | HMRC may issue a P800 and repay, or you claim |
| Overpaid and no P800 arrived | Claim it yourself, do not wait |
| More than four tax years ago | Out of time, nothing can be claimed |
The bit HMRC does not spell out
The four year limit is strict and it is quiet. There is no reminder, no warning letter, and no discretion once the window closes. Every April a year drops off the end and whatever was owed in it is gone permanently.
If you suspect any of the last four years was wrong, check now rather than at some convenient future point. This is the single most valuable habit in this course, and it takes an afternoon at most.
What a P800 is
A P800 is HMRC's own calculation after the tax year ends, saying you either overpaid or underpaid. It arrives automatically in some cases and not others. Receiving one is useful; not receiving one is not evidence that your position was correct.
Common mistakes
- Waiting for HMRC to notice. Many overpayments are never flagged.
- Assuming no P800 means no refund due. It does not.
- Letting the four year window close. There is no discretion afterwards.
- Paying an agent for a claim you can make free. The next course covers this.
Try it on your own numbers
This is the same calculator as the full tool page, using 2026/27 rates.
Could HMRC owe you money?
Answer a few quick questions to estimate a possible tax refund. Updates as you type.
Leave "tax paid" at 0 if you don't know it - we'll still check the reliefs below.
Tick any that apply to you:
A rough estimate only. Claim refunds free via your Personal Tax Account on gov.uk - never pay a percentage to a refund firm if you can claim it yourself.
You could be owed around
this year - up to with 4-year backdating
- Estimated this year
Estimate only - actual refunds depend on your full HMRC record.
Relief value by income
Your ticked reliefs are worth more at higher tax ratesTax relief is given at your marginal rate, so the same allowances are worth more once you're a higher-rate taxpayer. The marker shows where your income sits.
| Item | Basis | This year | 4-year |
|---|---|---|---|
| Total estimate | |||
Reliefs are given at your marginal rate ( on your current income). Marriage Allowance and emergency-tax refunds are fixed estimates. Backdating is generally available for up to 4 tax years.
Compare saved scenarios
| Scenario | This year | 4-year | |
|---|---|---|---|
Key takeaways
- ✓ Check the code number, its deductions, and the letter against your situation
- ✓ Corrections go through your Personal Tax Account and reach your employer quickly
- ✓ Overpayments can only be reclaimed for four tax years
- ✓ Not receiving a P800 does not mean your tax was right
Check you have got it
3 quick questions. No score is kept, and you can change your mind.
1. How far back can you reclaim overpaid PAYE?
2. You have not received a P800. What does that tell you?
3. You are still on an emergency code after three months. What should you do?
Sources
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