HMRC Tax Codes Explained: What Does Your Tax Code Mean?

Your tax code tells your employer or pension provider how much income tax to deduct from your pay. Getting it wrong means you could be overpaying or underpaying tax for months — or even years — before the mistake is caught. Yet most people have never checked their tax code, and few understand what the letters and numbers actually mean. In this comprehensive guide, we decode every common UK tax code, explain how HMRC calculates yours, and show you how to check and change it if it is wrong.

What Is a Tax Code?

A tax code is a combination of numbers and letters that tells your employer how much tax-free income you are entitled to in a tax year, and how to calculate your tax deductions. Your tax code appears on your payslip, P60, P45, and HMRC correspondence. It is unique to your circumstances and can change from year to year — or even mid-year — if your situation changes.

The number in your tax code represents your tax-free allowance. To get the actual allowance, multiply the number by 10. For example, a tax code of 1257L means you have a tax-free allowance of £12,570 — which is exactly the standard Personal Allowance for 2025/26. The letter(s) after the number tell your employer which tax calculation rules to apply.

Common Tax Codes Explained

1257L — The Standard Code

This is by far the most common tax code in the UK. It means you are entitled to the full standard Personal Allowance of £12,570 with no adjustments. If you have one job, no untaxed income, no benefits in kind, and no other complications, this is the code you should have. It has been the standard code since 2021/22 when the Personal Allowance was frozen.

BR (Basic Rate)

If your tax code is BR, your entire income from this source is taxed at the basic rate of 20%. This typically happens when you have a second job or pension and your Personal Allowance has already been allocated to your main income source. With a BR code, there is no tax-free amount — every pound is taxed at 20%.

If you believe you should not have a BR code (for example, if your main job has ended and this is now your only income), you should contact HMRC immediately to get your code updated. Operating on the wrong code for an extended period will result in over- or underpayment that needs to be corrected later.

D0 (Higher Rate) and D1 (Additional Rate)

These codes work like BR but at higher rates. D0 taxes all income at 40%, and D1 taxes all income at 45%. They are used for secondary income sources where the taxpayer's total income puts them in the higher or additional rate band. For example, if you earn £70,000 from your main job (coded 1257L) and £10,000 from a pension, the pension would typically be coded D0 because your combined income exceeds the basic rate band.

K Codes

A K code is unusual because it means you owe more tax than your Personal Allowance covers. Instead of a tax-free amount, additional tax is collected through your pay. The number after K represents the amount that must be added to your taxable income, divided by 10.

For example, K475 means £4,750 must be added to your taxable income. This can happen if you have significant benefits in kind (such as a company car or private medical insurance), if HMRC is collecting tax you owe from a previous year through your code, or if you owe tax on the State Pension.

Important: there is a regulatory safeguard that prevents a K code from collecting more than 50% of your gross pay in any pay period. If the K code calculation would exceed this, the excess is carried forward.

Emergency Tax Codes

Emergency tax codes are temporary codes applied when HMRC does not have enough information to issue the correct code. They are most commonly applied when you start a new job and your new employer has not received a P45 from your previous employer. The emergency codes for 2025/26 are:

• 1257L W1 (or M1) — Week 1 / Month 1 basis: tax is calculated on the current period's pay only, without reference to cumulative earnings. This means you get 1/12th (monthly) or 1/52nd (weekly) of the annual Personal Allowance each pay period.
• 1257L X — Similar to W1/M1 but used in specific circumstances
• BR W1 or 0T W1 — Emergency codes without any allowance

The “W1” or “M1” suffix means the code operates on a non-cumulative basis — each pay period is treated independently. This can result in overpayment of tax, especially early in the tax year. Once HMRC issues a correct cumulative code, your employer will adjust your tax to correct any over-deduction. If the adjustment does not happen automatically, you may need to claim a refund through Self Assessment or by contacting HMRC directly.

Scottish Tax Codes (S Prefix)

If you live in Scotland, your tax code will be prefixed with “S” (e.g., S1257L). This tells your employer to apply Scottish Income Tax rates, which differ from the rest of the UK. Scotland has six income tax bands compared to three for England, Wales, and Northern Ireland, with rates ranging from 19% (Starter Rate) to 48% (Top Rate).

Your status as a Scottish taxpayer is determined by where you live, not where you work. If you move from Scotland to England (or vice versa), you should notify HMRC so they can update your code accordingly.

Welsh Tax Codes (C Prefix)

Welsh taxpayers have a “C” prefix (e.g., C1257L). While the Welsh Government has the power to vary income tax rates, it has so far kept them aligned with England and Northern Ireland rates. The C prefix exists as a technical requirement to enable Welsh rate-setting, even though the rates are currently identical.

How HMRC Calculates Your Tax Code

HMRC calculates your tax code by starting with your total allowances and subtracting your total deductions. The formula is:

Tax Code Number = (Total Allowances - Total Deductions) ÷ 10

Total Allowances may include:
  • Personal Allowance: £12,570
  • Blind Person's Allowance: £3,070
  • Professional subscriptions
  • Flat rate expenses for your occupation
  • Marriage Allowance transfer received

Total Deductions may include:
  • Company car benefit (P11D value × CO2 percentage)
  • Private medical insurance benefit
  • Underpaid tax from previous years
  • State Pension (if receiving)
  • Other untaxed income
  • Marriage Allowance transfer given

For example, if you have the standard Personal Allowance (£12,570), a company car benefit of £5,000, and £2,000 of underpaid tax being collected, your code would be:

Allowances:  £12,570 (Personal Allowance)
Deductions: -£5,000 (company car)
            -£2,000 (underpaid tax collection)
            ────────
Net:         £5,570

Tax Code: 557L

How to Check Your Tax Code

There are several ways to check your current tax code:

• HMRC Personal Tax Account: Log in at gov.uk/personal-tax-account. This shows your current tax code for all employments and pensions, and lets you see how it was calculated.
• HMRC App: The free HMRC app (available on iOS and Android) shows your tax code and allows you to check the breakdown.
• Payslip: Your current tax code appears on every payslip.
• P2 Notice of Coding: HMRC sends this letter (or digital notification) whenever your tax code changes. It shows the full calculation.
• P60: Your end-of-year certificate shows the tax code that was in force at 5 April.

How to Change Your Tax Code

If you believe your tax code is wrong, you should act promptly. There are several ways to request a change:

• Online: Use your Personal Tax Account to update your income details, benefits, or allowances. HMRC will automatically recalculate your code.
• Phone: Call HMRC on 0300 200 3300 (Income Tax general enquiries). Lines are open Monday to Friday, 8am to 6pm.
• Check for Refunds: If you have overpaid tax due to a wrong code, HMRC may issue a P800 tax calculation at the end of the year, or you can claim a refund through Self Assessment.

Common situations requiring a tax code change include: starting or ending a second job, starting to receive a pension, company benefits changing (new company car, medical insurance), becoming entitled to Marriage Allowance, or moving between Scotland, Wales, and England.

Tax Codes with Multiple Jobs

If you have more than one job or pension, your Personal Allowance is split across your income sources. Typically, your main job gets the full allowance (1257L) and your other jobs are coded BR, D0, or D1. However, you can ask HMRC to split your allowance differently if that would reduce the overall tax burden.

For example, if you have two part-time jobs each paying £20,000, you could ask HMRC to split the allowance equally — giving each job a code of approximately 628L. This avoids the situation where one job taxes every pound at 20% while the other gives a full allowance. The total tax over the year is the same, but the cash flow is better.

Summary: What to Do Right Now

• Check your latest payslip for your current tax code
• Log into your HMRC Personal Tax Account to see the full breakdown
• Compare your code to the standard 1257L — if it is different, understand why
• If you think your code is wrong, contact HMRC immediately to avoid months of over- or underpayment
• Keep records of any tax code changes and the reasons for them
• Use TaxWhizz.ai to run a full tax position check and identify if your code is costing you money