Tax code checker calculator, 2026/27

How this is calculated

A standard tax code such as 1257L is read by multiplying the number by 10 and adding 9, giving an implied tax-free personal allowance of £12,579, which HMRC rounds in practice to the £12,570 standard allowance for 2026/27. Comparing the allowance implied by your code against this standard figure shows whether you are receiving more or less tax-free pay than the default, and the calculator estimates the basic-rate tax impact of any difference.

A K code works in reverse, adding to taxable pay rather than providing an allowance, and is used where deductions such as company benefits, previous underpaid tax, or other untaxed income exceed the available personal allowance entirely.

Common tax code letters and what they mean

The letter L is the standard suffix for someone entitled to the basic personal allowance. M and N relate to the marriage allowance transfer, BR means all income is taxed at basic rate with no allowance (often used for a second job), D0 means all income is taxed at higher rate, and 0T means no allowance is being given at all, often because HMRC lacks enough information. NT means no tax is deducted, which is unusual and specific to certain circumstances.

A tax code ending in W1 or M1 indicates a non-cumulative basis, commonly applied temporarily when starting a new job without a P45, and should generally be corrected to a cumulative code once HMRC has full details, or it can lead to an under or overpayment across the year.

What to do if your code looks wrong

If the allowance implied by your code does not match what you expect, check your latest HMRC tax code notice for the reasons given, such as company car benefits, untaxed savings interest, or a previous year's underpayment being collected through the code. You can update your details or query the code directly through your personal tax account or by contacting HMRC, and any correction is usually applied to future pay rather than backdated automatically.

What does the standard tax code 1257L mean?

It means you are entitled to the standard £12,570 tax-free personal allowance for 2026/27, applied cumulatively across the year, which is the default code for most employees with one job and no unusual deductions or benefits.

What is a K code and why do I have one?

A K code means deductions, such as untaxed benefits or previous tax owed, exceed your personal allowance, so the excess is added to your taxable income rather than reduced by an allowance, increasing the tax deducted each pay period.

Why might my tax code be different from a colleague's?

Tax codes reflect individual circumstances, including benefits in kind, additional income, marriage allowance transfers, or corrections for previous years, so two people on the same salary can legitimately have different codes.

How do I get my tax code corrected?

Check the reasons shown on your HMRC tax code notice, then update or query your details through your personal tax account online or by contacting HMRC directly; corrections are usually applied prospectively rather than backdated.