Why Has My Tax Code Changed?

If your tax code has changed, it usually means HMRC has updated how much tax-free income you are entitled to, or how your tax is being collected. Common triggers include starting a new job, receiving a benefit in kind such as a company car, taking on a second income, owing tax from a previous year, or a Marriage Allowance change.

In this insight we walk through the most common reasons your tax code changes, how each one affects your take-home pay, and how to check that the new code is right.

---

Key Takeaways

• Your tax code can change when your income, benefits, or allowances change, or when HMRC needs to collect tax owed from a previous year.
• A lower number often means less tax-free pay, for example because of a benefit in kind or tax owed, while a higher number means more.
• Codes like BR, D0 or 0T can appear when you take a second job or your allowance is reallocated between incomes.
• HMRC usually sends a coding notice explaining the change, and you can always check the reasons in your personal tax account.

---

HMRC Sends You a Coding Notice

When your tax code changes, HMRC normally issues a PAYE coding notice, form P2, which sets out your new code and the reasons behind it. Your employer also receives the new code and applies it to your next available payday.

The notice breaks down how your tax-free amount is worked out, including any additions and deductions. If you have not received one but your payslip shows a new code, you can view the details in your personal tax account on GOV.UK. For a refresher on how codes are built, see our guide to tax codes explained.

Starting or Changing Jobs

A change of job is one of the most common reasons your code moves. When you leave a role, your P45 passes details to your next employer, and HMRC reallocates your Personal Allowance to the new job.

If you start a job without a P45, you may be placed on an emergency tax code until HMRC has your full details. Once everything is in place, your code should settle onto the correct cumulative version, often the standard 1257L for a single job.

Benefits in Kind

If you receive taxable benefits through work, such as a company car, fuel, or private medical insurance, these count as extra income. Rather than taxing them separately, HMRC usually reduces your tax-free allowance to collect the tax through your code.

That is why a benefit in kind often lowers the number in your code below the standard figure. When the benefit changes or ends, your code is adjusted again. You can see the impact of these changes on your take-home using our income tax calculator.

A Second Income

Taking on a second job or a second pension frequently changes your codes. Your Personal Allowance is normally applied to your main income, while the second source is taxed with a code such as BR at 20%, D0 at 40%, or 0T with no allowance.

If your incomes shift in size, HMRC may reallocate your allowance between them, which changes both codes. Our guide to the tax code for a second job explains how this works and how to split your allowance if it suits you.

Underpaid Tax and Allowance Changes

There are a few other common reasons a code changes:

• Underpaid tax. If you owe tax from a previous year, HMRC may collect it by reducing your tax-free allowance, lowering your code number for the year.
• Marriage Allowance. Transferring part of your allowance to or from a partner changes your code, shown by an M or N letter.
• Change in income above £100,000. The Personal Allowance tapers away for higher incomes, which can reduce your code.
• Expenses or reliefs. Claiming job expenses or certain reliefs can increase your tax-free amount and raise your code.

If you have a student loan, that does not change your tax code, but it is deducted separately, as explained in student loan repayment.

How to Check the New Code Is Right

Start by reading the coding notice or checking your personal tax account, which lists each addition and deduction. Compare it against your circumstances: does the benefit shown match what you actually receive, and is your allowance in the right place?

If something looks wrong, contact HMRC to correct it. Because an incorrect code can mean paying too much or too little, it is worth a few minutes to confirm. You can explore more planning tools on our calculators page.

Frequently asked questions

Why did my tax code go down?

A lower code usually means less tax-free pay. Common causes are a new or increased benefit in kind, tax owed from a previous year being collected through your code, or your allowance being reallocated to another income. Your coding notice or personal tax account will show the exact reason.

Does a new tax code mean I will pay more tax?

Not always. Some changes increase your tax, such as a benefit in kind, while others reduce it, such as claiming expenses or receiving Marriage Allowance. The direction depends on whether your tax-free amount has gone up or down, which the coding notice explains.

My tax code changed but nothing changed in my life. Why?

Occasionally HMRC updates a code based on estimated figures, an old benefit still on record, or a mistaken second employment. If you cannot see why it changed, check your personal tax account and contact HMRC, as it may need correcting.

How often can my tax code change?

There is no fixed limit. HMRC can update your code whenever your circumstances change or new information arrives, which may be several times in a year. Many people also see a routine change ahead of a new tax year in April.

General information only, not financial advice. If you think your tax code is wrong, contact HMRC.