Tax Code Calculator
Decode your HMRC tax code for 2025/26. Find out what each part means, see the impact on your monthly pay, and get step-by-step help fixing common tax code problems.
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How to Use This Calculator
Decode My Tax Code tab
Enter any HMRC tax code (e.g. 1257L, S1257L, BR, K500) and the calculator breaks it down: what the number means, what the letter means, whether it includes a Scottish (S) or Welsh (C) prefix, and whether emergency tax (W1/M1) applies. It shows your effective Personal Allowance and flags anything unusual.
Impact on Pay tab
Enter your tax code and gross salary to see exactly how much income tax you pay per month and per year under your current code. The calculator compares this against the standard 1257L code so you can see if you are overpaying or underpaying and by how much.
Common Problems tab
Select from five common tax code problems — BR on a main job, emergency W1/M1, K codes, wrong country prefix, and 0T with no allowance. Each scenario explains what is happening, shows a worked example with real numbers, and gives step-by-step instructions to fix it.
Share your result
Every input is encoded in the URL. Click Share to send your exact scenario to an accountant, employer, or save it for later reference.
How UK Tax Codes Work
Your tax code tells your employer how much income tax to deduct from your pay. It is set by HMRC and usually appears on your payslip, P45, P60, and HMRC coding notice (P2).
Number in tax code × 10 = your annual tax-free Personal Allowance
Example: 1257L → 1257 × 10 = £12,570 tax-free allowance
Decoding the letter:
L = standard Personal Allowance
M = Marriage Allowance recipient (+10% of partner's PA)
N = Marriage Allowance transferor (-10% of your PA)
T = HMRC is making other adjustments
BR = all income taxed at 20% (no allowance)
D0 = all income taxed at 40%
D1 = all income taxed at 45%
NT = no tax deducted
0T = no Personal Allowance applied
K = negative allowance (deductions exceed your PA)
Prefixes:
S = Scottish taxpayer (6 tax bands, up to 48%)
C = Welsh taxpayer (same rates as England for 2025/26)
Suffixes:
W1 / M1 / X = emergency (non-cumulative) basis
The standard code for 2025/26 is 1257L, giving everyone the £12,570 Personal Allowance. If you earn over £100,000, your allowance is reduced by £1 for every £2 above £100,000 and reaches £0 at £125,140.
Example
Sarah — Marketing Manager, 34, Bristol
Sarah earns £42,000 and has just started a new job. Her payslip shows tax code 1257L M1 (emergency). She wants to know what this means and how much extra tax she might be paying.
Decode tab
Sarah's code gives her the correct £12,570 allowance, but the M1 suffix means each month is calculated independently. She should provide her P45 to her new employer so HMRC can issue a cumulative code.
Impact on Pay tab
With the correct cumulative 1257L code, Sarah pays £5,886 in income tax per year (£491/month). The emergency M1 code gives the same monthly amount but cannot make mid-year adjustments, so she should get it corrected promptly.