Has your pay been fine for months, then suddenly a lot more tax comes off? Often the cause is your tax code. It tells your employer or pension provider how much of that income is tax-free.
Where to find it
your payslip
the HMRC app
the "Check your Income Tax" online service on GOV.UK
a "Tax Code Notice" letter from HMRC
What the numbers mean
The numbers are the tax-free amount for that income, with the last digit replaced by a letter.
1257L: £12,570 tax-free, and L means the standard Personal Allowance. This is the most common code for people with one job.
Lower number? HMRC takes untaxed income or benefits off your allowance. For example, if your employer gives you medical insurance worth £1,570, your allowance becomes £12,570 − £1,570 = £11,000 and your code becomes 1100L.
What the letters mean
Letter
Meaning
L
Standard Personal Allowance
M
Marriage Allowance: you've received 10% of your partner's allowance
N
Marriage Allowance: you've transferred 10% of your allowance to your partner
T
Other calculations are involved in working out your allowance
0T
Your allowance has been used up, or you've started a new job
BR
All income from this job or pension is taxed at the basic rate (20%)
D0
All income from this job or pension is taxed at the higher rate (40%)
D1
All income from this job or pension is taxed at the additional rate (45%)
NT
No tax is taken from this income
K
Your untaxed income is more than your Personal Allowance
An extra letter at the start: S means Scottish rates and C means Welsh rates. The percentages in the table are the rates for England and Northern Ireland. Scotland's rates are different.
W1, M1 or X at the end? That's an emergency code
For example 1257L W1, 1257L M1 or 1257L X. Your payslip might also say "NONCUM".
When you get one: you start a new job without giving your employer a P45, or you start getting company benefits or the State Pension.
What happens: tax is worked out on that week's or month's pay alone, as if you were paid that amount all year, so it's often wrong.
What to do: give your P45 to your new employer. HMRC usually updates your code within 35 days. You can get back any tax you overpaid.
Why your tax code might change
Common reasons:
you start a new job, or have an extra job or pension
you start getting taxable state benefits
your savings interest goes over your Personal Savings Allowance
your State Pension changes
your employer tells HMRC your benefits have changed
you claim Marriage Allowance, or tax relief on work expenses
you have to pay the High Income Child Benefit Charge
you were on the wrong code before and owe tax
Readers ask: after six months, tax is suddenly taken at 20% with no allowance
Your code has probably changed to BR or 0T, or you're on an emergency code. Check the code on your payslip, then sign in to "Check your Income Tax" to see the reason HMRC has recorded.
If you think your code is wrong
Sign in to the "Check your Income Tax" online service, or use the HMRC app.
Check your job, pension, estimated income, company benefits and expenses, and update anything that's wrong.
HMRC updates your code and tells you and your employer within 15 working days. If you're paid monthly, your next or following payslip should show the change.
If you can't use the online service, contact HMRC. If you've just started a new job, wait 35 days first so HMRC has your new income details.
You can claim back tax you overpaid, and you'll need to pay any tax you owe.
Sources checked: 1 October 2026 · Tax year: 2026 to 2027 · Sources are official GOV.UK pages.
This is general information, not tax advice for your situation. How it applies depends on your full circumstances.