You can change your tax code online in minutes or by calling HMRC. Here are the 3 methods, what to tell them, how long the change takes, and how to claim back any overpaid tax.
You do not need to live with a wrong tax code. HMRC lets you request a change online, over the phone, or by letter, and the fastest method takes less than 10 minutes. Once the change is processed, your employer receives the new code automatically and adjusts your pay. If you have been overpaying, the correction is applied cumulatively, meaning you get the overpaid tax back through your next pay packet. This guide covers all three methods, exactly what HMRC needs from you, and how to get a refund for past overpayments.
You cannot change your tax code directly -- only HMRC can issue a new code. But you can tell HMRC that your circumstances have changed, and they will calculate and issue the correct code. Here are the three ways to do that, from fastest to slowest.
The online route is the quickest. Most changes submitted this way are processed within 2 to 3 weeks, and you can do it at any time of day.
Step-by-step:
Once processed, HMRC sends a P6 notice to your employer electronically. Your employer does not need to take any action -- their payroll system picks up the new code and applies it in the next pay run. You will also receive a P2 coding notice explaining the new code.
Why this is the best option: It is available 24/7, it creates a digital record of your request, and HMRC's online systems process changes faster than phone or letter requests. You can also track the status of your change through the same account.
If you prefer speaking to someone, or if the online system does not cover your specific situation, call the Income Tax helpline.
Contact details:
Before you call, have this ready:
What happens on the call: The HMRC agent reviews your record, asks you to confirm details, and can often update your code while you are on the line. You will receive a confirmation letter (P2 coding notice) within a few days, and your employer receives the P6 electronically.
Tip: Call early in the morning (8am) or late in the afternoon (after 4pm) for shorter wait times. Mondays and the days immediately after bank holidays are the busiest.
Timeline: The code change is processed during or shortly after your call. Your employer typically receives the P6 within 1 to 2 weeks. Expect to see the new code on your payslip within 2 to 3 weeks of calling.
Writing to HMRC is the slowest option but may be necessary if you need to send supporting documents or if the other methods are not accessible.
Write to:
Pay As You Earn and Self Assessment HM Revenue and Customs BX9 1AS
Include in your letter:
Timeline: Allow 4 to 6 weeks for HMRC to process a written request. You will receive a P2 coding notice by post confirming the change, and your employer will receive a P6 electronically.
When to use this method: If you need to send evidence that cannot be uploaded online (for example, a letter from a foreign tax authority or a legal document), a written request is the appropriate route. For everything else, Method 1 or 2 is faster.
Regardless of which method you use, HMRC needs the same core information to process a code change:
Always required:
Required depending on your reason:
| Reason for change | What HMRC needs |
|---|---|
| Old employer still on record | Employer name, leaving date, P45 details if available |
| Company car returned | Date returned, car make/model, list price |
| Benefits in kind ended | Type of benefit, date it ended |
| Student loan fully repaid | Repayment date, loan type (Plan 1, 2, or 4) |
| Marriage Allowance claim | Partner's National Insurance number, marriage/civil partnership date |
| Income estimate wrong | Corrected income estimate for the tax year |
| Moving to/from Scotland | New address and date of move |
| Second job started or ended | New employer details, or confirmation of leaving |
Knowing your desired code: You do not need to tell HMRC what code you want. Give them the facts about your circumstances and they calculate the correct code. However, if you have worked out that your code should be 1257L (standard Personal Allowance, no adjustments), mentioning this can speed up the process.
The timeline depends on the method and the complexity of the change:
| Method | HMRC processing time | Employer receives P6 | Shows on payslip |
|---|---|---|---|
| Online (Personal Tax Account) | 1 to 2 weeks | 2 to 3 weeks from submission | Next pay date after P6 received |
| Phone (0300 200 3300) | During or after the call | 1 to 2 weeks from call | Next pay date after P6 received |
| Letter | 3 to 4 weeks | 4 to 6 weeks from posting | Next pay date after P6 received |
Important: The new code applies from the next pay date after your employer receives the P6. If your employer runs monthly payroll on the 25th and the P6 arrives on the 20th, your March payslip will show the new code. If the P6 arrives on the 26th, you will have to wait until April.
How to confirm the change was applied: Check your next payslip after the expected timeline. The tax code field should show the new code. If it still shows the old code after a full pay cycle following the expected P6 delivery, contact your payroll department. In rare cases, the P6 may not have been processed by their system, and they can apply the code manually.
If you are self-employed and juggling PAYE alongside Self Assessment, keeping track of code changes and their impact on your overall tax bill is critical. TapTax consolidates all your income sources and tax obligations, so a PAYE code change is automatically reflected in your Self Assessment picture. Track your tax with TapTax.
Starting a new job is the most common trigger for a tax code change. How smoothly it goes depends on whether you have a P45 from your previous employer.
With a P45:
Your P45 tells your new employer your tax code, total pay, and total tax deducted in the current tax year. They enter these details into their payroll system and continue using the same code. HMRC receives the information through Real Time Information (RTI) and confirms or updates the code. In most cases, nothing further is needed from you.
Without a P45 (most common source of problems):
If you do not have a P45 -- because you lost it, your previous employer has not issued it, or this is your first job -- your new employer asks you to complete an HMRC Starter Checklist. Based on your answers, they apply one of three codes:
If your employer does not have your P45 or a completed Starter Checklist, they default to an emergency code (usually 1257L W1/M1 or 0T). This almost always results in overpayment.
What to do after starting: Check your payslip after your first two pay periods. If you see W1, M1, X, or an unexpected code:
Do not assume it will sort itself out. Emergency codes do not automatically convert to cumulative codes -- HMRC needs information from you or your employer to make the switch.
If you have been on a wrong code for weeks or months, you have overpaid tax. Here is how you get that money back.
Current tax year -- automatic payroll refund:
When HMRC issues a new cumulative code, your employer's payroll system recalculates your year-to-date tax. The difference between what you paid and what you should have paid is refunded in your next pay packet. If you were on BR for four months when you should have been on 1257L, that is roughly £840 in overpaid tax (4 months at £210/month on a £25,000 salary) coming back in a single pay.
This can make one month's take-home pay significantly higher than usual. Do not be alarmed -- it is your money being returned.
Current tax year -- large overpayments:
If the overpayment is very large (for example, you were on BR for an entire year and the correction happens in March), your employer may not be able to refund the full amount in one pay period because it would exceed the tax already collected. In this case, the refund is spread across remaining pay periods, or HMRC issues a direct repayment.
Previous tax years -- P800 refund:
After each tax year ends on 5 April, HMRC reconciles your records. If you overpaid, they send a P800 tax calculation (usually between June and November). The P800 tells you how much you are owed. You can claim the refund online through your Personal Tax Account (paid within 5 working days) or wait for a cheque by post (within 60 days).
Previous tax years -- Self Assessment refund:
If you file a Self Assessment return, overpaid PAYE tax from a wrong code is factored into your return. The overpayment reduces your Self Assessment bill or generates a refund. You can amend a return for a previous year if the original did not account for the wrong code.
The four-year window: You can claim back overpaid tax for up to four tax years. In 2025/26, that covers 2021/22 through to the current year. Do not leave money unclaimed, especially if you have been on a wrong code for an extended period. For full details on the refund process, see our guide on what to do if you have a wrong tax code.
Most overpaid tax from a wrong code is refunded automatically once the correction is made. But if HMRC has not caught the error, you need to report it yourself. The sooner you act, the sooner you stop overpaying.
Not all code changes require you to take action. HMRC proactively updates codes in several situations:
After filing Self Assessment. When HMRC processes your Self Assessment return, they may adjust your PAYE code for the following year. For example, if your return shows rental income, HMRC may reduce your allowance to collect tax on that income through your pay. This is normal and avoids a large Self Assessment bill at year end.
After P11D reporting (benefits in kind). Every July, employers submit P11D forms to HMRC listing the benefits in kind provided to each employee (company cars, medical insurance, loans, etc.). HMRC uses this information to adjust your code for the current year. If your employer reported a new company car, your allowance decreases. If a car was returned, it increases.
At the start of a new tax year (January to March). HMRC issues new coding notices for the upcoming tax year between January and March. These reflect any known changes, estimated income adjustments, and carried-forward underpayments. Check the P2 coding notice carefully -- if HMRC's estimates differ from your actual situation, request a correction before the new tax year starts.
After government benefit changes. If you start or stop receiving certain taxable benefits (such as the State Pension or Jobseeker's Allowance), HMRC updates your code to account for the change in taxable income.
What to watch for with automatic changes: HMRC's automatic updates are based on information they have at the time, which may be outdated or estimated. If you receive a P2 notice with a code you do not expect, check it immediately. Automatic changes are not always correct, and you have the right to challenge them using the methods above.
Related guides: Wrong tax code? What to do --> | How to check your tax code -->
Related tax codes: 1257L tax code | 0T tax code | BR tax code | W1 tax code
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