Your situation
Wrong tax code: how to spot it and get it fixed
Independent site, not HMRC. Only HMRC can change your code: use your HMRC online account or app.
Most wrong codes come from wrong or missing details at HMRC. Find the mistake, correct the record and follow the new code to your payslip.
Your situation points to
1100L
Your current code takes about £316.00 too little this year.
| Tax due for the year | £3,800.00 |
| Taken with 1257L | £3,484.00 |
| Taken with the expected code | £3,798.00 |
| Personal Allowance | £12,570 |
Estimate on employment and pension income only. HMRC sets your code from its own records; savings, property and other income can change it.
A tax code is usually wrong because HMRC has incorrect or missing information about your jobs, pensions, benefits or expenses, not because of a payroll error. The quickest fix, as GOV.UK sets out, is to sign in to the Check your Income Tax online service, review your employment and pension details, the estimated taxable income, any company benefits and expenses, and correct what is wrong. If a change is needed, HMRC updates the code and tells both you and your employer within 15 working days. Monthly paid staff should see it on their next or the following payslip; weekly paid staff on the third. The error can be costly: an only job of £30,000 wrongly coded BR loses the £12,570 Personal Allowance and pays £2,516.00 too much over a year, while a second job wrongly on 1257L leaves a debt for later. After starting a new job, allow 35 days for HMRC to receive your details before you contact it.
Two codes on the same pay
BR against 1257L, over the year
+£2,516.00
| Tax with 1257L | £3,484.00 |
| Tax with BR | £6,000.00 |
| Each month | £209.67 |
Rules read on HMRC’s texts by Radif Partners · Editorial policy · Method
Signs that your code does not fit your situation
Start with the code on your latest payslip and ask whether it describes your year. The usual mismatches are easy to spot once you know them:
- a second job or pension shows a code with a number instead of BR or a D code, so both sources are giving you an allowance;
- your only job shows BR or 0T, so no allowance is given at all;
- the code still ends in W1, M1 or X more than 35 days after you started, which the emergency code guidance treats as a sign the code may still be wrong;
- a company car or medical insurance has started or stopped and the number has not moved;
- you claimed job expenses or Marriage Allowance and the number or letter has not changed;
- the code is built on an old salary or on a job you have left.
The tool at the top builds the code your situation points to and sets it against the code you have, so you can see the gap before you sign in anywhere.
What a wrong code costs over a year
The table compares several codes with 1257L on a single job of £30,000, using the 2026 to 2027 rates for England and Northern Ireland. A code that gives too little allowance overcharges every month; one that gives too much leaves a shortfall.
| Code used | Tax over the year | Against 1257L |
|---|---|---|
| BR | £6,000.00 | +£2,516.00 |
| 0T | £6,000.00 | +£2,516.00 |
| D0 | £12,000.00 | +£8,516.00 |
| 1100L | £3,798.00 | +£314.00 |
| 1383M | £3,232.00 | −£252.00 |
The opposite mistake is just as common with two jobs. With £28,000 from a main job and £7,000 from a second, both coded 1257L, payroll takes £3,084.00 over the year while £4,486.00 is due, leaving £1,402.00 to be collected later through your code. The second job guide explains which code each source should carry.
Codes for two jobs
Expected codes
1257L + BR
| Tax due for the year | £4,486.00 |
| Second job with 1257L by mistake | £0.00 |
| Second job with its expected code | £1,399.80 |
Correcting the record with HMRC
HMRC normally updates codes from what employers and pension providers report, so a wrong code points to a wrong record. Fix the record and the code follows. In the Check your Income Tax service:
- sign in, or create sign-in details if you have none; you may be asked to prove your identity with photo ID;
- check each employment and pension listed, the taxable income HMRC estimates for the year, and any company benefits and expenses;
- update anything wrong or missing, such as a job that has ended or a salary that has risen;
- claim tax relief on employment expenses if you pay for things your job requires.
If you left a job and never received a P45, ask the former employer for one: it carries the pay, tax and code HMRC needs. Without access to the online service, you can contact HMRC instead.
From new code to corrected payslip
Once HMRC changes the code, it tells you and your employer within 15 working days. Payroll then has to load it: on monthly pay you should see it on the next or the following payslip, and on weekly pay by the third. If it does not appear, the first check is with your employer, who may not have processed the notice yet.
A cumulative code applied mid-year recalculates the tax on all your pay since 6 April, so the first payslip on the new code often carries the correction in one go. If you paid too much, the refund after a wrong code usually arrives that way; if HMRC still lacks some income details, the balance is settled after the tax year ends instead.