Understanding PAYE and your UK tax code
PAYE — Pay As You Earn — is the system HMRC uses to collect Income Tax and National Insurance Contributions directly from your wages or pension before you receive them. Your employer or pension provider deducts the correct amount each pay period using a tax code issued by HMRC, meaning most employees never need to file a Self Assessment return. Understanding how that code works helps you catch errors before they accumulate into a larger underpayment or overpayment.
How PAYE collects tax
Under PAYE, HMRC calculates your expected tax liability for the year and divides it across your pay periods. Each time you are paid, your employer applies the current tax code to determine how much to deduct. The deductions are sent directly to HMRC. At the end of the tax year, HMRC reconciles the total deducted against the actual liability; if too much was taken, you are due a refund, and if too little was taken, you may receive a P800 tax calculation showing a balance to pay.
National Insurance Contributions are calculated separately on each pay period's earnings and follow their own rate structure, independent of the tax code.
How to read a tax code
A tax code is typically a number followed by a letter — for example, 1257L. The number represents the amount of tax-free income you are entitled to in the year, divided by ten. So 1257 indicates a tax-free allowance of £12,570, which corresponds to the standard Personal Allowance.
The letter modifies how the code is applied:
| Letter | Meaning |
|---|---|
| L | Standard Personal Allowance |
| M | Marriage Allowance received (from a partner) |
| N | Marriage Allowance transferred (to a partner) |
| T | HMRC needs to review your code; various adjustments apply |
| BR | All income from this source taxed at the basic rate (no allowance here) |
| D0 | All income taxed at the higher rate |
| D1 | All income taxed at the additional rate |
| NT | No tax deducted from this income source |
| K | Your untaxed income exceeds your allowances; an amount is added to your income |
Emergency codes — often followed by "W1", "M1", or "X" — are applied when HMRC does not yet have enough information. These treat each pay period in isolation rather than on a cumulative basis, which can lead to over- or under-deductions that are corrected once a full code is issued.
Why tax codes change
HMRC adjusts tax codes throughout the year in response to new information. Common triggers include:
- Starting or leaving a job or pension
- Receiving benefits in kind from an employer (a company car, for instance, reduces the tax-free allowance)
- Claiming or stopping Marriage Allowance
- HMRC becoming aware of untaxed income — such as rental income or savings interest — that needs to be collected through PAYE rather than a separate bill
- Corrections to an earlier under- or over-deduction
Your employer is notified of any change via a tax code notice (P6 or P9 form sent electronically), and the new code takes effect from the next pay run. You should also receive a PAYE coding notice (P2) by post or through your Personal Tax Account online.
Checking your tax code with HMRC
You can review your current and previous tax codes, and see the breakdown of how they were calculated, through your Personal Tax Account at gov.uk/personal-tax-account. The account also allows you to update certain details — for example, claiming the Marriage Allowance or reporting a change in employment — which triggers an automatic recalculation.
If you believe a code is wrong, you can contact HMRC directly. Employers cannot change a tax code on their own; all adjustments originate with HMRC.
Common problems to watch for
- Multiple jobs or pensions: your Personal Allowance is usually allocated to your main income source. Additional sources are often coded BR (basic rate on all earnings from that source). If your combined income takes you above the higher-rate threshold, those sources may need to use a higher-rate code.
- Cumulative vs week 1/month 1 codes: a cumulative code catches up throughout the year; an emergency or "W1/M1" code does not. If you are on an emergency code for several months, you may face a correction at year end.
- Benefits in kind: the taxable value of employer-provided benefits reduces your tax-free allowance in the code. If the benefit changes mid-year, the code should be updated; verify it was.
If your circumstances are complex — multiple income streams, overseas elements, or significant benefits — a qualified tax professional can review whether your code accurately reflects your position.
Where to get help
A qualified tax professional can interpret your tax code, identify potential errors, and liaise with HMRC on your behalf. Find accredited professionals on TaxProsRated through the recognised professional bodies for the UK.
Sources
HM Revenue and Customs (HMRC) — PAYE and tax codes guidance: https://www.gov.uk/tax-codes