Tax Code Wrong code Explained

Your tax code can be wrong if HMRC has out-of-date information – for example about a previous job, a benefit you no longer get, or estimated income. GOV.UK says it is your responsibility to check you're paying the right tax. If the code is wrong, you can update your details online, and any overpaid tax is refunded through payroll or after the year ends.

How your pay is taxed on Wrong code

A wrong code changes your tax every payday. Example (England, £30,000): on 1257L you pay about £290.50 a month; on BR or 0T (no allowance) you'd pay £500 – £209.50 too much each month, or £2,514 over a full year. In the other direction, two jobs both using 1257L can leave you owing tax at year end.

Tax-free allowance from this code£12,570Cumulative

Income tax with this code	£3,486
Income tax with standard 1257L	£3,486
Difference per month	£0.00

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Why you might have this code

HMRC thinks you still have an old job or pension using your allowance.
A company benefit (car, medical insurance) has ended but is still in your code.
Your estimated pay, savings interest or other income is out of date.
Your employer applied the wrong code or hasn’t updated it.

What to do

Find your code: personal tax account, HMRC app, your payslip or a Tax Code Notice letter.
Check HMRC’s breakdown of how it was worked out.
Update details online: change your income estimate, remove an ended benefit, or tell HMRC about a job that has stopped.
If you can’t fix it online, contact HMRC’s Income Tax helpline with your National Insurance number and employer’s PAYE reference.
Once HMRC issues a new code, your employer applies it and refunds any overpayment through your pay; otherwise HMRC sends a P800 after 5 April.

See all tax codes or check your take-home with the UK salary calculator.

Match the symptom to the likely cause

What you notice	Likely cause	What to do
Tax jumped after starting a new job	Emergency code (M1, W1, X, 0T or BR)	Give payroll your P45 or a starter checklist; wait 35 days, then update HMRC
Second job taxed at 20% but the first job pays under £12,570	Allowance all on the main job	Ask HMRC to move the unused allowance to the second job
Code still includes a company benefit you no longer get	Employer hasn’t told HMRC the benefit stopped	Update the benefit in the Check your Income Tax service
Code has no S or C but you live in Scotland or Wales (or the reverse)	Old address	Update your address; the change is backdated to 6 April
Earning over £100,000 but still on 1257L	HMRC hasn’t applied the taper	Update your income estimate to avoid a bill
Code lower and HMRC mentions interest	Estimated savings interest too high	Correct the estimate, especially after moving money into an ISA

How long a correction takes

HMRC tells you and your employer the new code within 15 working days of updating it.
If you’re paid monthly, it should show on your next payslip or the one after. If you’re paid weekly, it should show on your third payslip. If it doesn’t, ask payroll whether they’ve received it.
HMRC stops sending codes to employers after 13 March. A mistake found in late March is usually put right through the year-end P800 rather than through pay.
P800 letters go out between June and March after the tax year. Refunds claimed online are paid within 5 working days. If HMRC sends a cheque automatically, it arrives within 14 days of the letter.

If HMRC won’t change it: objecting formally

You have a formal right to object to a coding notice at any time during the year. HMRC’s manual tells staff to explain the figures and to leave a disputed amount out of the code if deductions would start before the dispute is settled and the objection seems fair. If you still can’t agree, you can appeal to the tribunal. HMRC can accept a better estimate from you – its guidance says it often will if the difference is small.

Someone can act for you: friends and family can register as a “trusted helper”, and agents can use HMRC’s PAYE Coding Notice query form.

If the wrong code means you owe tax

HMRC normally collects an underpayment through next year’s code if it’s less than £3,000 and you have enough PAYE income. Larger amounts, or tax that can’t be collected through your code, come as a Simple Assessment bill with a payment deadline. You can also pay before the new tax year starts so your code isn’t reduced.

Frequently asked questions

What tax code should I be on?

One job, no benefits: 1257L (S1257L in Scotland, C1257L in Wales). Second job: usually BR, D0 or 0T. Marriage Allowance: 1383M or 1131N. Anything else should be explained in HMRC's breakdown.

How do I get a refund for a wrong tax code?

Once corrected, payroll usually refunds overpayment in your next pay. If not, HMRC reconciles your tax after the year ends and sends a P800 if you're owed money.

Can my employer change my tax code?

Only HMRC decides your code. Your employer must apply what HMRC sends.

How far back can I claim overpaid tax?

Generally up to four tax years.

What is a P800?

A tax calculation HMRC sends after the year ends if you paid too much or too little through PAYE.

How long does HMRC take to fix a tax code?

HMRC sends the new code to you and your employer within 15 working days. If you’re paid monthly, it should appear on your next payslip or the one after.

Can I formally appeal against my tax code?

Yes. You can object to a coding notice at any time in the year. If you can’t reach agreement with HMRC, the dispute can go to the tax tribunal.

Can someone else sort out my tax code for me?

Yes. A friend or relative can register as a trusted helper, and a tax agent can use HMRC’s PAYE Coding Notice query form.

Will correcting my tax code change my National Insurance?

No. Tax codes only control Income Tax. National Insurance is worked out on your pay by each employer, whatever your code.

Can I stop HMRC collecting tax I owe through my code?

Yes. You can pay before the new tax year starts. If the debt is from Self Assessment, you can also say on your tax return that you don’t want it collected through your code.

HMRC says it sent a new code but my payslip hasn’t changed. What now?

If you’re paid monthly, allow for the next payslip or the one after; if weekly, your third. If it still hasn’t changed, GOV.UK says to ask your employer whether they’ve received the new code.

Sources

Figures are taken from official government publications and were last reviewed on 2026-10-03.