How to Change Your Tax Code - 3 Methods, HMRC Contact Details, and Key Documents

To change your tax code, contact HMRC online through your Personal Tax Account, by phone on 0300 200 3300, or by post. HMRC overcharged more than 5 million workers £3.5 billion in income tax in 2023-24 due to incorrect PAYE coding, according to analysis by accountancy group UHY Hacker Young. Checking and correcting a tax code takes under 5 minutes online.

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What Is a Tax Code?

A tax code is used by an employer or pension provider to calculate how much income tax to deduct from pay or pension. HMRC issues the code directly to the employer. The standard personal allowance tax code for the 2025-26 tax year is 1257L, representing a tax-free personal allowance of £12,570.

Tax codes apply to all workers under the Pay As You Earn (PAYE) system. The Office for National Statistics estimates that coding notices affect approximately 30 million PAYE taxpayers annually.

What Do Tax Code Letters Mean?

Tax code letters indicate specific personal tax circumstances, such as whether a taxpayer is using the Marriage Allowance or pays the additional rate of 45%. Examples include:

• L - Standard personal allowance
• M - Marriage Allowance received from a partner
• N - Marriage Allowance transferred to a partner
• BR - All income taxed at basic rate (20%)
• D0 - All income taxed at higher rate (40%)
• K - Tax owed exceeds the personal allowance
• NT - No tax deducted

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Why Would a Tax Code Need Changing?

There are 7 common reasons a tax code requires a change. These include starting a new job, receiving taxable state benefits, earning from an additional job or pension, changes to the weekly State Pension, starting or stopping job benefits, claiming Marriage Allowance, and claiming expenses for tax relief.

Incorrect assumptions by HMRC about a worker's additional income, such as rental income, dividends, or freelance work they are no longer doing, are a further reason a taxpayer may receive the wrong tax code. Confusion over how many jobs an individual holds and outdated employer payroll data are also common causes.

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How Do You Change Your Tax Code?

To change your tax code, sign into your HMRC Personal Tax Account at gov.uk, update your income details, and submit. HMRC will issue a revised coding notice to your employer. There are 3 methods available.

How Do You Change Your Tax Code Online?

Sign into your Personal Tax Account at gov.uk, select "Check your Income Tax," update your income or allowances, and submit. HMRC processes most online requests within 2 working days.

Steps to change a tax code online:

1. Go to gov.uk and sign in using your Government Gateway credentials

2. Select "Check your Income Tax"

3. Review your current tax code and listed income sources

4. Update any incorrect income figures or allowances

5. Submit the changes

6. Wait for HMRC to notify you and your employer of the revised code

What Do You Need to Access Your HMRC Personal Tax Account?

You need 2 things: a Government Gateway user ID and your National Insurance number. If you do not have an account, you can create one using your National Insurance number and a valid form of ID.

How Do You Change Your Tax Code by Phone?

Call HMRC on 0300 200 3300, Monday to Friday, 8am to 6pm, with your National Insurance number and employment details ready.

For complex cases or corrections not reflected online, contact HMRC at 0300 200 3300. Have your National Insurance number, P45, P60, and recent payslips ready.

How Long Do You Wait on the Phone With HMRC?

HMRC phone wait times can start at 10 minutes and may exceed an hour during business hours. January to April are the busiest periods.

How Do You Change Your Tax Code by Post?

Write to HMRC PAYE, BX9 1AS, including your National Insurance number, employer details, and the reason for the change. Postal requests take up to 8 weeks to process.

Postal submissions are suitable for multi-year coding errors or corrections that cannot be completed through the online service.

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What Documents Are Needed to Change a Tax Code?

There are 4 documents that support a tax code change request. Each applies to a different correction scenario.

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How Long Does a Tax Code Change Take?

A tax code change takes between 2 working days and 8 weeks, depending on the method used.

Processing times by method:

• Online via Personal Tax Account: 2 working days
• Phone request: 5 to 10 working days
• Employer-initiated change via P6 notice: within 1 payroll cycle
• Postal request: up to 8 weeks

HMRC will issue a notification to inform both the taxpayer and the employer of a tax code change. The taxpayer is likely to receive a paper letter. The employer will also be notified and must update payroll accordingly.

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What Happens If Your Tax Code Is Wrong?

A wrong tax code results in either overpayment or underpayment of income tax. HMRC will contact a taxpayer if their tax code changes. However, if HMRC holds incorrect income information, the taxpayer may carry an incorrect code without being notified.

Approximately 5.6 million taxpayers were affected by incorrect tax codes in 2023-24, with an estimated £3.5 billion overpaid to HMRC. Many affected workers remain unaware of the issue, as the discrepancy appears within payroll deductions rather than as a separate tax demand.

The average overpayment for a worker on the wrong tax code is £689, research shows.

How Do You Claim a Refund From a Wrong Tax Code?

Contact HMRC by phone on 0300 200 3300 or online after receiving a P800 letter to claim a refund. If you have overpaid tax, this will be repaid either through your next pay or at the end of the tax year when you receive your P800. Overpaid tax can be reclaimed for up to 4 prior tax years.

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How Do You Check If Your Tax Code Is Correct?

Check your tax code on your most recent payslip, P60, or through your Personal Tax Account at gov.uk. Cross-reference the code against your total income, personal allowance, and any active benefits or allowances.

Use these 4 checks to verify your PAYE code:

1. Confirm the personal allowance reflects £12,570 for 2024-25

2. Check that all income sources, including second jobs and pensions, are recorded

3. Verify that benefits in kind, such as a company car or private health insurance, are correctly reflected

4. Confirm that Marriage Allowance is applied if eligible

The National Audit Office reported that in 2022-23, more than 1.9 million taxpayers received tax code corrections or refunds following post-year-end reconciliation.

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What Are the 5 Most Common Tax Code Mistakes?

There are 5 common tax code mistakes. Examples include:

1. Carrying a previous employer's code into a new job without providing a P45

2. Leaving an emergency code such as 0T or 1257L W1 uncorrected across multiple pay periods

3. Failing to report the removal of a benefit in kind, such as a company car

4. Not claiming Marriage Allowance, which is worth up to £252 per year

5. Ignoring a P800 letter, which results in an outstanding tax debt

HMRC's coding assumptions often go unchecked because paper tax code notices are no longer routinely issued. This means millions of employees may be unaware that their tax code is wrong and that they are being overcharged.

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How to Change Your Tax Code - Summary

To change a tax code, use 1 of 3 methods: the HMRC Personal Tax Account at gov.uk, a phone call to 0300 200 3300, or a postal submission to HMRC PAYE, BX9 1AS. Online changes process within 2 working days. Incorrect PAYE codes affected 5.6 million UK workers in 2023-24, producing £3.5 billion in overpaid income tax. Workers can reclaim overpaid tax for up to 4 prior years after identifying a coding error.