How to Check and Correct Your HMRC Tax Code
How to check your HMRC tax code online and fix mistakes easily. Follow our simple steps to correct tax code errors and avoid overpaying tax in 2026/27.
Your tax code determines how much Income Tax your employer deducts from your pay. If your code is wrong, you could be overpaying by hundreds of pounds or underpaying and facing a tax bill later.
Fortunately, checking your tax code online is quick and free. You can fix most errors directly through HMRC without needing to call anyone.
This guide explains how to check your tax code, what the different codes mean, why they can be wrong, and how to correct them quickly and safely.
Use our Income Tax Calculator to see how much tax you should be paying once your code is corrected.
For a detailed breakdown of the most common tax code, our 1257L tax code guide explains what it means and how it applies to you. If you are unsure about emergency tax codes, our emergency tax codes guide covers how to spot and fix them.
Your tax code tells your employer how much of your income is tax-free. A wrong code can mean overpaying tax. Checking it through your HMRC Personal Tax Account is quick and free.
What Is a Tax Code
A tax code tells your employer or pension provider how much tax-free income you can earn each year before Income Tax applies.
The most common tax code is 1257L. The number 1257 represents your Personal Allowance of £12,570. The letter L means you are entitled to the standard allowance.
HMRC uses your code to calculate how much Income Tax should be taken from your salary under the PAYE system. Your employer applies this code to each payslip throughout the tax year.
If your circumstances change, your tax code may be adjusted. Common adjustments include changes to your Personal Allowance, benefits in kind, Marriage Allowance, or underpaid tax from previous years.
For a complete list of tax codes, the list of UK tax codes covers every code you might see on your payslip.
Your tax code is a combination of numbers and letters. The numbers represent your Personal Allowance, and the letters indicate your circumstances. The standard code is 1257L.
Why Checking Your Tax Code Matters
Your tax code can change without you realising it. This often happens when you change jobs, receive company benefits, claim Marriage Allowance, or get a pay rise.
If your tax code is wrong, you might overpay tax and miss out on money that is yours, or underpay and face a bill from HMRC later. Overpayments are more common, but both situations can be avoided by checking your code regularly.
Checking your tax code takes a few minutes and could save you a significant amount of money. It is one of the simplest financial checks you can do.
If you have changed jobs recently, our guide to sudden tax code changes explains the common triggers.
A wrong tax code can cost you money or lead to unexpected tax bills. Checking it regularly helps you catch errors early.
Where to Find Your Tax Code
You can find your current tax code on several documents. The most common places are your payslip, P60, P45, and your HMRC Personal Tax Account.
| Document | Where to Look | Example Code |
|---|---|---|
| Payslip | Usually top right or under PAYE section | 1257L |
| P60 | Year-end summary of income and tax | 1257L |
| P45 | When you leave a job | 1257L or BR |
| HMRC Personal Tax Account | Online via GOV.UK | Full history and breakdown |
If your code looks unfamiliar, such as 0T, BR, or 1257L M1, it may need correction.
Our PAYE payslip guide explains how to read your payslip and find your tax code.
Your tax code appears on your payslip, P60, P45, and HMRC Personal Tax Account. If it looks unfamiliar, it may be wrong.
How to Check Your Tax Code Online
Checking your tax code online through HMRC's Personal Tax Account is the most accurate and reliable method.
Step 1: Visit the GOV.UK Personal Tax Account page
Go to the GOV.UK website and search for Personal Tax Account.
Step 2: Sign in or register
You will need a Government Gateway ID. If you do not have one, registration takes about five minutes. You will need your National Insurance number and a form of ID such as a passport or P60.
Step 3: Select Pay As You Earn (PAYE)
Once logged in, choose PAYE under the Income Tax section. You will see your current and previous tax codes, the employers or pensions linked to each, and how HMRC calculated your tax-free allowance.
Step 4: Compare it to your payslip
If the tax code on your payslip does not match what is in your HMRC account, your employer may be using an old or emergency code, which could lead to overpayment.
Check your tax code through your HMRC Personal Tax Account. You can view your current code, see how it was calculated, and compare it to your payslip.
Common Tax Codes and What They Mean
Understanding common tax codes helps you identify when something is wrong.
| Tax Code | Meaning | When It's Used |
|---|---|---|
| 1257L | Standard Personal Allowance (£12,570) | Most employees |
| 1257L M1/W1 | Emergency tax (Month 1/Week 1) | New job or missing P45 |
| BR | Basic Rate (20%) on all income | Second jobs or pensions |
| 0T | No Personal Allowance | Allowance used elsewhere |
| D0 | 40% Higher Rate | Second income for higher earners |
| NT | No tax deducted | Tax-free income cases |
| K Codes (e.g. K125) | Negative allowance | You owe tax from prior adjustments |
If you see M1/W1, BR, or 0T on your main job, it is a sign you may be overpaying until HMRC updates your record.
Our emergency tax codes guide explains how to resolve these codes.
Common codes include L for standard allowance, BR for second jobs, D0/D1 for higher rates, and M1/W1 for emergency tax. If you see BR or 0T on your main job, you may be overpaying.
Why Your Tax Code Might Be Wrong
Even small life or job changes can trigger code errors. Here are the most common reasons.
| Cause | What Happens | How to Fix It |
|---|---|---|
| New job or missing P45 | Emergency tax code applied | Submit your P45 or update HMRC online |
| Multiple jobs | Allowance applied to wrong employer | Contact HMRC to assign correctly |
| Benefits in kind | Company car, health plan, etc. alter your allowance | Update benefit details in HMRC account |
| Marriage Allowance | You or your partner transferred allowance | Ensure both accounts show M or N code |
| Leaving a job mid-year | Code may not reset properly | Contact HMRC for correction |
| Pension income | Pension providers sometimes apply old codes | Update provider details via HMRC |
If your tax code has changed suddenly, our guide to sudden tax code changes explains the common triggers.
Tax codes are often wrong because of job changes, outdated HMRC records, or incorrect benefit reporting. Checking your code is the only way to know for sure.
How to Correct a Wrong Tax Code
Once you have identified an incorrect code, you can fix it quickly through your Personal Tax Account.
Step 1: Log in to your Personal Tax Account
Go to the GOV.UK website and sign in to your Personal Tax Account.
Step 2: Report a change or error
Look for the option to Check your Income Tax or Tell us about a change. You can correct employer or pension details, add or remove benefits, update estimated income, or confirm your Marriage Allowance status.
Step 3: Wait for an updated code
HMRC usually issues a new code within 5 to 10 working days. Your employer will receive it automatically and apply it to your next payslip.
Step 4: Check your next payslip
Make sure your new code appears. If it does not, speak to your payroll department or contact HMRC directly on 0300 200 3300.
For more on fixing tax codes, our how to check your tax code online and fix mistakes guide covers the process in detail.
You can fix most tax code errors by reporting changes through your Personal Tax Account. HMRC will issue a new code, and your employer will apply it on your next payslip.
How Long Does It Take to Correct a Tax Code
The time it takes to correct a tax code depends on how you make the correction.
- Online update via HMRC: Usually 5 to 10 working days
- By phone: Can be faster, sometimes immediate
- Through employer: Changes reflect in 1 to 2 pay cycles
If you have overpaid, HMRC may adjust it through payroll, which means you get a refund on your payslip, or issue a P800 refund or Simple Assessment by post.
Use our Income Tax Calculator to estimate how much you might be owed.
Online corrections usually take 5 to 10 working days. Phone corrections can be faster. Your employer will apply the new code on your next payslip.
Example: Fixing a Wrong Tax Code
Amira changes jobs but forgets to give her P45 to her new employer. She is put on 1257L M1, meaning emergency tax is applied. Her monthly pay is £250 lower than expected.
Amira logs into her Personal Tax Account and reports that her previous job ended. HMRC updates her record within a week. Her next payslip shows the correct 1257L code, and she gets a refund on her following payday.
This is a common scenario, and it is easily fixable by checking your tax code and reporting changes.
A wrong tax code can be fixed by reporting changes through your Personal Tax Account. Once corrected, overpaid tax is usually refunded through your payslip.
Preventing Future Tax Code Errors
Once you have fixed your tax code, there are steps you can take to avoid future errors.
- Always submit your P45 when starting a new job – This prevents emergency tax codes
- Check your HMRC account twice a year – Catches mistakes early
- Inform HMRC about job or benefit changes – Keeps records up to date
- Use online calculators to compare – Ensures correct take-home pay
- Keep your P60 and payslips – Useful for refunds or audits
Our Income Tax Calculator can help you double-check your tax each year.
Prevent future errors by providing your P45 to new employers, checking your payslip regularly, and updating HMRC when your circumstances change.
When to Contact HMRC Directly
You may need to call HMRC if your employer has not applied the new code after 6 weeks, you receive a P800 or Simple Assessment you do not understand, you have multiple income sources such as jobs and pensions, or you believe you are being taxed on the wrong income.
HMRC Income Tax Helpline: 0300 200 3300
Opening hours: Monday to Friday, 8am to 6pm
Contact HMRC if your employer has not applied a new code after 6 weeks, or if you receive a tax calculation you do not understand.
Final Thoughts
Your tax code is one of the most important factors in determining how much tax you pay. Checking it online through your HMRC Personal Tax Account is quick, free, and essential for ensuring you pay the correct amount.
If your code is wrong, you could be overpaying or underpaying tax. Common errors happen after job changes, benefits updates, or Marriage Allowance changes. You can fix most errors by reporting changes online. If you have overpaid, you can claim a refund through your account or by contacting HMRC.
Check your tax code regularly, especially after any change in circumstances, to ensure you are paying the correct amount. Use our Income Tax Calculator to verify your deductions once your code is corrected.
All information in this guide is based on official HMRC and GOV.UK sources. Readers should verify their tax code through their HMRC Personal Tax Account before making financial decisions, as individual circumstances vary and rules may change after publication.
Written by
Daniel Reed
Daniel Reed writes about PAYE, payslips, tax codes, workplace deductions and take-home pay in the UK.
See more from Daniel Reed