K tax codes explained
A K in your tax code means you have income or deductions, such as a company car or tax owed from an earlier year, that are more than your tax-free Personal Allowance and aren't already taxed. Instead of tax-free pay, a K code adds an amount to your taxable pay. Your employer can't take more than half of your pay before tax.
Enter your own K code to see how it changes income tax and take-home pay.
Try a K code in the calculatorHow a K code is worked out
The number works like any other code, times £10, but in reverse: K475 adds about £4,759 a year to your taxable pay, or £396.59 a month.
Example, month 1: pay £1,000 plus £396.59 is £1,396.59 of taxable pay, rounded down to £1,396, taxed at 20%: £279.20.
The 50% limit
However large the K code, the tax taken in one pay period can't be more than half of that period's pay. On a normal (cumulative) code, tax held back by the limit is collected in later pay periods when there's room.
Common reasons for a K code
- Paying tax you owe from a previous year through your wages.
- State Pension or taxable state benefits.
- Company benefits, such as a company car.
- Savings interest above your Personal Savings Allowance.
Questions
Why do I have a K tax code?
Because income you're not yet taxed on is bigger than your tax-free allowance, so HMRC collects the difference through your pay.
Can a K code take all my wages?
No. Tax in any pay period can't be more than half of your pay before tax for that period.
Sources
- GOV.UK — Tax codes: if you have a K in your tax code
- HMRC — Specification for PAYE Tax Table Routines, version 24.0
Official sources checked 24 September 2026. This guide explains how pay documents work; it is not tax or legal advice.