How to Change Your Tax Code: Four Routes, One Goal

HMRC changes your tax code without asking you. Changing it back requires you to ask them. That asymmetry costs UK employees hundreds of millions of pounds every year, quietly drained from payslips by codes that nobody corrected.

If you are searching for how to change your tax code, you already suspect something is wrong. Good instinct. The question is which route gets it fixed fastest, and how far back you can claim what you are owed.

Tax Code

A combination of letters and numbers issued by HMRC to your employer or pension provider, instructing them how much income tax to deduct from your pay. The number represents your tax-free allowance divided by ten; the letters modify it based on your personal circumstances. A wrong code means the wrong amount of tax is deducted, often without you realising.

Why Your Tax Code Might Need Changing

Before picking up the phone to HMRC, it helps to know why your code went wrong in the first place. The most common culprits are:

A job change. When you move employer, HMRC sometimes issues an emergency tax code (1257L W1 or M1, or the dreaded BR) until it can confirm your details. Emergency codes treat every pay period in isolation, ignoring your cumulative allowance, which almost always results in overpayment.

A benefit in kind. Company car, private medical insurance, a free parking space at work. HMRC reduces your personal allowance to collect tax on these perks through your code. If the benefit changes or disappears and HMRC is not told, the old reduction stays put.

State pension. HMRC often collects tax on the State Pension by reducing the tax code on a private pension or employment income. If those figures shift, the arithmetic stops working.

Multiple jobs. Your full personal allowance (£12,570 for 2024/25) is typically assigned to one employer. If HMRC allocates it incorrectly, one job overtaxes you and another under-taxes you simultaneously.

Student loan or Child Benefit. HMRC adjusts codes for High Income Child Benefit Tax Charge when household income exceeds £60,000 (from April 2024). If your income dropped below that threshold, the adjustment may still be sitting in your code.

None of these errors reflect a personal failing on your part. HMRC's systems rely on information flowing automatically from employers, pension providers, and DWP. When that information is delayed, wrong, or simply not passed on, your code suffers. As our post Your Wrong Tax Code Is Costing You Money Right Now covers in detail, the financial impact compounds month by month.

If you are not certain what your current code means, Tax Code Numbers: What Each Digit Actually Means breaks down the notation clearly before you take any action.

The Four Routes to Change Your Tax Code

Route 1: Your Personal Tax Account Online (Fastest)

This is almost always the fastest option and the one HMRC itself now pushes hardest. Go to gov.uk/personal-tax-account, sign in with your Government Gateway credentials, and navigate to "PAYE Income Tax" or "Check your tax code."

From there you can:

• View the code currently applied to each employment or pension
• See the breakdown of what is included (allowances, deductions, benefits)
• Tell HMRC directly if information is wrong, for example if a benefit in kind has changed or your employment status is different

For simple corrections, HMRC's system updates your code digitally and instructs your employer within days. Your next payslip should reflect the change. There is no queue, no waiting on hold, and no risk of being cut off after twenty-two minutes.

You can also check your tax code free at /check-my-tax-code before logging into the Government Gateway, which is a useful first step to confirm whether your code looks correct before deciding what to tell HMRC.

Route 2: Phone HMRC's Income Tax Helpline

For more complex situations, a phone call to HMRC's Income Tax helpline (0300 200 3300, Monday to Friday, 8am to 6pm) allows you to speak to an adviser who can investigate the underlying reason for the code and correct it on the spot.

This route is better when:

• You have multiple jobs or pension sources and the allocation is wrong
• You believe HMRC has been told something incorrect by a previous employer
• You want to confirm a refund is being processed, not just a future code change

Be patient. Call volumes are highest Monday mornings and in the weeks following payslip cycles. Mid-week, mid-morning is traditionally quieter. Have your National Insurance number, most recent payslip, and the P60 (or P45) from any relevant previous employer to hand.

HMRC will issue a PAYE Coding Notice (P2) confirming the new code. Keep it. If a future payslip still shows the old code, the notice is your evidence that the employer is using outdated information.

Route 3: Write to HMRC by Post

Slow, but occasionally necessary when supporting documents need to accompany your request, such as proof that a company car was returned, evidence of a change in childcare arrangements, or documentation of a rental income figure that HMRC has estimated incorrectly.

Send to: Pay As You Earn and Self Assessment, HM Revenue and Customs, BX9 1AS.

Always write your National Insurance number and, if you have one, your UTR (Unique Taxpayer Reference) at the top. Keep a copy of everything you send. HMRC's own service standard for post is fifteen working days, though in practice backlogs can stretch that considerably.

Route 4: Ask Your Employer's Payroll Department

Your employer cannot change your tax code themselves. That instruction must come from HMRC. But your payroll department can:

• Confirm which code they are currently using and whether they have received a recent P9 (coding notice) from HMRC
• Flag to HMRC that the code looks anomalous, sometimes triggering a faster review
• Apply emergency adjustments if HMRC instructs them to

If your code changed unexpectedly after a pay review or new benefit was introduced, ask payroll whether a P11D was submitted and what figure HMRC was given. Errors at the P11D stage are a common source of incorrect codes that persist for a full tax year.

What Happens After You Request a Change

Once HMRC processes your request, they issue a new P2 Coding Notice to you and a P9 instruction to your employer. The new code applies from the next payroll run, which is typically your next pay date.

Here is the part most people miss: a new code fixes the future but does not automatically recover the past. If you have been overpaying for six months because your code was wrong, that overpayment sits with HMRC until the end of the tax year, when it is usually refunded automatically through the P800 reconciliation process.

If you do not want to wait until after 5 April, you can request an in-year refund by contacting HMRC directly and citing the corrected code. There is no guaranteed timeline, but HMRC does process these and can issue a cheque or bank transfer within a few weeks.

For overpayments in previous tax years (up to four years back), you must make a formal claim. HMRC will not volunteer refunds for years it considers closed. You can do this through your Personal Tax Account or by writing in. The four-year window runs from 31 January following the relevant tax year: for 2020/21, that means the claim deadline is 31 January 2026.

The Scenario Nobody Warns You About

Sarah is an NHS administrator earning £38,000. In April last year she started receiving a small private pension of £4,200 annually. HMRC correctly identified this and adjusted her employment tax code downward to collect the tax due on the pension. Fine.

But HMRC estimated her pension figure at £5,800 based on projected growth that never materialised. Her employment tax code was reduced by £158 too much, costing her roughly £32 per month in overpaid tax. Over twelve months: £384.

Sarah received a P800 in July confirming a refund was due, which was reassuring. But if she had checked her code in May and spotted the discrepancy, she could have requested an in-year corrected code and received that £384 spread back across her payslips rather than waiting fourteen months for a lump sum.

Checking your code is not a one-time task. HMRC revises codes throughout the year, and Your Tax Code Is a Message from HMRC. Can You Read It? explains how to decode whatever lands in your post or Personal Tax Account each time they do.

If HMRC Will Not Change Your Code

Rarely, HMRC will maintain a code you believe is wrong because they are acting on information they consider accurate from a third party (an employer, a pension provider, DWP). In that case:

1. Ask HMRC what information they hold and where it came from. You have the right to know.
2. Go to the source. If a previous employer filed an incorrect P60 or P11D, contact their payroll or HR team and ask them to submit a correction directly to HMRC.
3. Submit a formal appeal. HMRC's decisions on PAYE coding can be formally disputed; their guidance at gov.uk/tax-overpayments-and-underpayments covers the process.

If the amount in dispute is significant and the process stalls, the Low Incomes Tax Reform Group (LITRG) and Citizens Advice both offer free guidance on escalating tax code disputes.

One Check You Can Do Right Now

You do not need to call HMRC, write a letter, or wait for your next P2 to start this process. Check your tax code at /check-my-tax-code to see whether your current code looks right for your circumstances before you take any next step.

If the number does not match your expected Personal Allowance (£12,570 for 2024/25, giving a standard code of 1257L), or if the letters suggest an emergency or non-standard arrangement, that is your signal to dig deeper through your Personal Tax Account or by calling HMRC.

You started searching for how to change your tax code because something felt off. That instinct is usually right. The four routes above give you everything you need to act on it today.

People also ask

How long does it take HMRC to change a tax code?

Once HMRC processes your request, they issue an updated code to your employer, typically within a few days if done online through your Personal Tax Account. Your next payslip should reflect the change. Postal requests can take up to fifteen working days, sometimes longer during peak periods.

Can I change my tax code myself without calling HMRC?

Yes. The quickest way is through your Personal Tax Account at gov.uk/personal-tax-account, where you can report changes to your income, benefits, or employment and HMRC will update your code digitally. You can also check your current code for free at /check-my-tax-code before taking action.

Will changing my tax code get me a refund for months I was overpaying?

A corrected code stops the overpayment going forward, but does not automatically trigger an immediate refund for past months. HMRC usually reconciles the year through a P800 notice after 5 April. If you want money back sooner, contact HMRC to request an in-year refund once your code has been corrected.

What is an emergency tax code and how do I get rid of it?

An emergency tax code (such as 1257L W1, 1257L M1, or BR) is applied when HMRC cannot confirm your full tax details, often after starting a new job. It means your allowance is not being spread correctly across the year, usually resulting in overpayment. Contact HMRC through your Personal Tax Account or helpline, providing your P45 from your previous employer, and they will issue the correct cumulative code.

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