The X Tax Code Explained.

Yes. The X code operates as an emergency or non-standard tax code. This means HMRC is treating your income differently from a standard worker, which very often results in you paying far more tax than you actually owe.

If this is your main or only job, you are almost certainly overpaying tax right now. X is a non-cumulative emergency code, applied regardless of pay frequency. Same implications as M1 or W1 — your tax is calculated independently each pay period, not cumulatively. However, if this is a second job, the X code might actually be perfectly correct.

HMRC typically issues the X code when they are missing crucial information about you. This usually happens if you start a new job without handing in a P45, if your employer uses the wrong starter checklist, or if HMRC suspects you owe tax from a previous year.

Your employer cannot fix your tax code for you. You must contact HMRC directly. The fastest way is to log into your Personal Tax Account on the GOV.UK website and update your estimated income. Alternatively, you can call HMRC on 0300 200 3300. If you have overpaid tax while on the X code, HMRC will usually automatically refund it in your next payslip once the code is corrected.

The amount of tax you pay depends entirely on your salary, but the X code drastically alters how much of that salary is tax-free. You can use our interactive calculator on this page to type in your exact salary and see instantly how much tax the X code is taking from your wages.