Coding notice breakdown
What is in my tax code, and why?
When HMRC changes your code they send a P2 “Tax Code Notice”. It lists what is added to your Personal Allowance and what is taken away. Copy each line in below and we will explain it, redo the sums, and tell you whether it matches the code on the letter.
Nothing you type here leaves your browser. If you cannot find your notice, it is also in your Personal Tax Account under “Check your Income Tax”.
About you
The lines on your notice
Copy each line from the P2, with its amount. Allowances are added; deductions are taken away.
The figures on the notice are allowances, not money
Every line is an amount of income you can have before tax (£12,570 of Personal Allowance, for example), or an amount taken off that. Nothing on the notice is money paid to you or owed by you. A deduction collects tax at your rate: a £2,500 reduction of allowances at 20% collects £500 of tax. Copy each figure exactly as printed and we show what it really means.
Personal Allowance
Added
£
Add a line
We will check whether the lines you entered add up to it.
Your lines add up to
1257L
- Allowances
- £12,570
- Deductions
- £0
- Tax-free pay a year
- £12,579
- Per month
- £1,048.25
How HMRC gets to that code
- Add up the allowances: £12,570.
- Add up the deductions: £0.
- Take one from the other: £12,570 − £0 = £12,570.
- HMRC drops the last digit: £12,570 becomes 1257.
- Your code is 1257L. That gives you £12,579 of tax-free pay this year, which is £1,048.25 a month.
What each line means
Personal Allowance
+ £12,570Everyone starts with the standard Personal Allowance of £12,570: the amount you can earn before paying tax. Everything else on the notice is added to or taken away from this figure.
Code shown as 1257L. Figures are for 2026/27.
In-year adjustments
Changed part-way through the year? You may have underpaid since April
A tax code is built for a whole tax year and spread evenly over the 12 months (or 52 weeks). If a change only reaches your code after 6 April, the paydays already gone were taxed on the old code, and nothing in your payslip goes back to correct them.
That applies to any change to your allowances or deductions: a company car or another benefit, a P11D deduction, a pension or other untaxed income starting, expenses or an allowance ending, or pay going over £100,000 so the Personal Allowance shrinks. If it went into your code at any point after April, the chances are you have been underpaying since April.
HMRC catches up with an in-year adjustment: the shortfall is worked out, grossed up and added to your code as “Estimated tax you owe this year”, spread over the paydays left. The new code is then issued on a week 1 / month 1 basis so that each remaining payday is taxed on its own. Enter your change below to see the amount and the code HMRC should send.
Your change
From the last payslip or notice before the change, for example 1257L.
The full-year figure on the notice, for example a car benefit of £2,000.
Usually April: benefits and income are coded for the whole year.
Month 1 is April (6 April to 5 May), month 12 is March. Your payslip shows it as the tax period.
Shows the change on your payslip and checks HMRC’s 50% limit.
We compare it with the code we work out.