HMRC may change your tax code when your income, benefits, pension, taxable expenses or other circumstances change, or when it updates an estimate of tax owed from an earlier year. The new code tells your employer or pension provider how much tax-free income to give you, so your take-home pay may rise or fall. Check the coding notice in your Personal Tax Account or app to see what HMRC has included and compare it with your circumstances. If anything is wrong, contact HMRC promptly and tell your employer or pension provider if HMRC issues a replacement code.