What Is a K Tax Code and Why Does It Mean You Pay More Tax?

If your payslip shows a tax code starting with K — like K497 or K832 — it means something unusual and potentially alarming is happening with your tax calculation. Unlike most tax codes that reduce the amount you pay tax on, a K code actually increases your taxable income.

How a K Code Works

A standard tax code like 1257L says: "Deduct £12,570 from your annual gross income, then apply tax rates to what's left." A K code reverses this logic. K497, for example, means HMRC is adding £4,970 to your income before calculating tax.

So if you earn £30,000 and have a K497 code, you pay tax as if you earn £34,970. At 20%, that's an extra £994/year — about £83/month — on top of what you'd normally pay.

Why Might You Have a K Code?

K codes arise when your total deductions from your personal allowance (due to benefits, underpayments, etc.) exceed the allowance itself. Common causes:

• A company car with high CO2 emissions that creates a large benefit-in-kind
• A significant underpayment from a previous year being collected through your code
• Multiple benefits-in-kind whose value exceeds your personal allowance
• Living accommodation provided by your employer
• State pension or other income that HMRC collects tax on through your PAYE code

The K Code Protections

HMRC places limits on K codes to prevent employers from deducting more than 50% of your gross pay in tax. This "50% overriding limit" means you should never take home less than half your pay due to a K code alone.

Is My K Code Right?

Log into your Personal Tax Account and review the breakdown of what HMRC says is reducing your allowance. If you've returned a company car, ended a benefit-in-kind, or disagree with the underpayment amount, contact HMRC to challenge it.

Frequently Asked Questions

Is a K code permanent?

No. K codes are reassessed each tax year. If the benefit-in-kind ends (e.g., company car returned) or the underpayment is cleared, the code reverts to a standard L code.

Can my K code be wrong?

Yes — K codes are particularly prone to error when employers submit P11D benefit values late or inaccurately, or when underpayments from previous years are estimated rather than calculated precisely. Always check what's driving the K using your tax account.

Use our Tax Code Checker to see what your K code means for your monthly tax bill.