How to Change Your Tax Code (and How Long HMRC Takes)

To change your tax code you tell HMRC what has changed — a new job, a benefit that has stopped, expenses you can claim, a second income that has ended — using the HMRC app, your Personal Tax Account or the Income Tax helpline. You cannot change the code yourself and neither can your employer: HMRC issues a revised code, sends it to your payroll, and your employer applies it on the next pay run after they receive it. In practice that usually means the corrected code lands on your payslip within one to two pay cycles, and any tax you overpaid earlier in the same tax year normally comes back through payroll rather than as a separate refund.

• Only HMRC can issue a tax code. Your employer must use the code they are given until a new one arrives.
• Updating your details in the HMRC app or online is the fastest route; phoning can sometimes get the code changed during the call.
• Expect one to two paydays before the new code shows up, depending on your employer's payroll cut-off.
• Moving from BR to 1257L is worth up to £2,514 of tax a year, because BR gives you no Personal Allowance at all.
• Overpaid tax from earlier years is repaid after a P800 calculation, and you can go back four tax years.

Is your code wrong?

Start with the code itself. It appears on your payslip, your P45, your P60 and in the HMRC app. The number is your tax-free allowance divided by ten, so 1257L means £12,570 of tax-free pay — the full Personal Allowance for 2026/27. The letters explain how the rest is taxed.

Codes starting with S apply Scottish rates to non-savings income, and C codes apply Welsh rates. Scotland has six bands in 2026/27, so a Scottish flat-rate code such as SD1 taxes that income at the higher Scottish rate of 42% rather than 40%.

Signs your code needs changing

• You only have one job but the code is BR, D0 or 0T.
• Your take-home pay fell sharply with no pay change.
• A company car, private medical cover or other benefit has ended but is still reducing your allowance.
• You have two codes that both include an allowance, so £12,570 is being given twice.
• A K code appeared and you do not know why.

Run your code through the tax code checker to see the allowance it gives you and the tax it produces on your salary, and read tax codes explained for what each letter does.

Change it in the app, online or by phone

All three routes lead to the same place: HMRC's PAYE record for you. You are not editing the code, you are correcting the information the code is built from.

The HMRC app

Sign in with your Government Gateway details, open your Pay As You Earn or Income Tax section and you can see your current code, the income sources it is split across, and the deductions in it. From there you can remove a job you no longer hold, correct an estimated pay figure, tell HMRC a company benefit has stopped, or add expenses such as professional subscriptions. Submitting a change triggers HMRC to recalculate and reissue the code.

Online

The same functions sit in your Personal Tax Account through Check your Income Tax for the current year. This is the better route if you need to see how your allowance has been divided between two jobs, or ask for more of it to be set against one of them.

By phone

If the problem is not one of the options on screen — a duplicate employment record, a K code you cannot explain, tax owed you dispute — use the Income Tax helpline. An adviser can often amend the record while you are on the call.

Have to hand: your National Insurance number, your payslip or P60, the name and PAYE reference of each employer, and the date anything changed. If you started a job without handing over a P45, giving your employer a completed starter checklist is often all it takes.

How quickly it takes effect

There are two clocks. The first is HMRC recalculating and issuing the code, which for an app or online change is usually a matter of days, and for a phone call can be immediate. The second clock is your employer.

HMRC sends the new code to your employer electronically as a P6 notice. Payroll teams pick these up on a schedule and have a cut-off date before each pay run — often a week or more before payday. If your new code arrives after that cut-off, it will not be used until the following month. So:

• Best case: you phone mid-month, the code is issued the same day, payroll picks it up and your next payslip is right.
• Typical case: the change misses one payroll cut-off and applies from the payday after — so one to two pay cycles.
• Slower case: HMRC needs information from your employer, or two employment records have to be merged, which adds time.

You do not need to wait for the paper coding notice (form P2) to arrive in the post; the electronic version reaches payroll first. If two full paydays pass with no change, check in the app that the new code was actually issued, then ask payroll whether they have received it.

BR to 1257L: what the change is worth

BR stands for basic rate. It taxes every pound at 20% and gives you no Personal Allowance, which is correct for a second job where your allowance is already used up, and expensive if it is your only job.

Worked example. Salary £30,000, paid monthly, England:

• On BR: £30,000 × 20% = £6,000 tax for the year, or £500 a month.
• On 1257L: £30,000 − £12,570 = £17,430 taxable × 20% = £3,486, or £290.50 a month.
• Difference: £2,514 a year — exactly £12,570 × 20%.

Now assume the correction reaches payroll in month 6. You have paid 6 × £500 = £3,000, but the tax due on a cumulative 1257L code by month 6 is 6/12 × £3,486 = £1,743. Payroll refunds the £1,257 difference in that payslip, so your take-home pay that month jumps by around £1,547 (the £1,257 refund plus the £290.50 reduction in that month's deduction). That only happens if the new code is cumulative. On a W1 or M1 code, each payday is treated separately, so nothing is refunded until the code becomes cumulative or the year ends.

National Insurance is unaffected by your tax code. It is worked out afresh each pay period on earnings above £12,570 a year at 8% up to £50,270, then 2%, whatever code you are on.

Getting overpaid tax back

Same tax year

If the code is fixed before 5 April and it is cumulative, the refund comes through your wages automatically, as in the example above. No claim form, no waiting for a cheque.

Earlier tax years

Once a year has closed, HMRC reconciles the PAYE records it holds and issues a P800 calculation or a simple assessment if you have paid too much or too little. Most of these go out between June and the following March. If a P800 shows a repayment you can usually claim it online and receive a bank transfer within about five working days, or wait for a cheque if you do nothing.

You do not have to wait to be contacted. You can ask HMRC to review a closed year, and you have four years from the end of the tax year to claim — so during 2026/27 the oldest year still open is 2022/23, which closes on 5 April 2027. That matters if you spent a year on BR or 0T and never noticed.

A wrong code cuts both ways. If your allowance was too generous, or a benefit was not coded, you may have underpaid instead, and HMRC normally collects that by reducing next year's code rather than asking for a lump sum. Our underpaid tax check walks through the usual causes.

One caution: if you also file a Self Assessment return, the return is what settles your final position for the year. Changing your code adjusts what you pay through the month; it does not change the tax ultimately due.

What to do next

Put your current code and salary into the tax code checker to see whether the allowance you are being given matches the one you are entitled to, and what the difference is worth each month. If the numbers look wrong, make the change in the HMRC app or through your Personal Tax Account, then check the next two payslips. If the problem stretches back over previous years, read tax codes explained and use the underpaid tax check before you contact HMRC, so you know which years to ask about.