How to Check Your Tax Code Online and Fix Mistakes
Check your tax code online with HMRC in 2026/27. Understand what your tax code means and follow these steps to fix errors and claim overpaid tax back.
If you have never checked your tax code, there is a reasonable chance it is wrong. Tax code errors are more common than many people realise and often occur because HMRC is working with outdated information. A wrong code either takes money out of your pocket through overpayment or leaves you with a tax bill you did not expect.
Checking your tax code online is one of the simplest things you can do to protect your finances. It takes a few minutes and is completely free. If you find an error, you can usually correct it without speaking to anyone on the phone.
This guide explains exactly how to check your code, what the numbers and letters mean, and what to do if you find a mistake.
Use our Income Tax Calculator to see what your deductions should actually be 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.
An incorrect tax code can cost you hundreds of pounds each year. Checking it online through your HMRC Personal Tax Account is quick, free, and one of the most important things you can do to protect your finances.
What Your Tax Code Actually Means
A tax code tells your employer how much of your income should be tax-free each month. It is made up of two parts: a number and a letter.
The number represents your Personal Allowance, which is the amount you can earn before paying Income Tax. At the time of writing, the standard Personal Allowance is £12,570. The number in your tax code represents this allowance with the last digit removed. For example, if your code is 1257L, the number 1257 means you have a Personal Allowance of £12,570.
The letter tells your employer whether you are on the standard allowance or if there is something different about your tax position.
- L – You are entitled to the standard Personal Allowance
- M – You have received a Marriage Allowance transfer from your partner
- N – You have transferred part of your allowance to your partner
- T – Your tax code includes other calculations or adjustments
- 0T – You have no Personal Allowance (often temporary)
- BR – All your income from this job is taxed at 20%
- D0 – All your income from this job is taxed at 40%
- D1 – All your income from this job is taxed at 45%
- NT – No tax is deducted from this income
If your code ends with M1 or W1, such as 1257L M1, you are on an emergency tax code. This often indicates HMRC is using temporary information and may result in paying too much tax.
For a complete list of tax codes and what they mean, our list of UK tax codes covers every code you might see on your payslip.
The number in your tax code represents your Personal Allowance. The letter indicates your specific circumstances. Codes ending in M1 or W1 often mean you are on emergency tax.
Why Your Tax Code Might Be Wrong
Tax codes are not automatically correct. Errors happen for several reasons, and most are not your fault.
The most common cause is starting a new job. If you do not give your new employer a P45, they may need to use temporary tax information until HMRC provides updated details. That temporary code often ignores part of your Personal Allowance, so you may end up paying more tax than you should.
Another common cause is changes to your income or benefits. If you receive a company car, private medical insurance, or other taxable benefits, HMRC should reduce your Personal Allowance to collect the tax. But if the benefit value is reported incorrectly or late, your code may not reflect the correct amount.
Marriage Allowance is another frequent source of errors. If you have transferred or received Marriage Allowance, your tax code should change to M or N. Many couples find this has not been applied correctly.
Sometimes HMRC simply holds outdated information. If you have moved house, changed jobs, or your income has changed, HMRC may not have updated your records.
If you have changed jobs recently, 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 Check Your Tax Code Online
You can check your tax code at any time through your HMRC Personal Tax Account. The process takes about five minutes.
Step 1: Log in to your Personal Tax Account
Go to the GOV.UK website and search for Personal Tax Account. You will need a Government Gateway ID. If you do not have one, you can create one during the sign-in process. You will need your National Insurance number and some personal details to verify your identity.
Step 2: Find your PAYE information
Once logged in, look for the Pay As You Earn (PAYE) section. This is usually under Income Tax. Click on it to see your current tax code and the employer it applies to.
Step 3: See how your code was calculated
There will be an option to view the breakdown of your tax code. Click on it. You will see your basic Personal Allowance, any additions for expenses or reliefs, and any deductions for benefits or underpaid tax. This breakdown tells you exactly why HMRC has assigned that particular code.
Step 4: Compare with your payslip
Look at your most recent payslip. Find your tax code. Compare it with what HMRC shows online. If they do not match, your employer may not have applied the latest update.
Step 5: Check previous years if you want
Your Personal Tax Account also shows past tax codes. If you think you have overpaid in previous years, this can help you identify when the error started.
For more on how to access and use your Personal Tax Account, our how to check and correct your HMRC tax code guide covers the process in detail.
Checking your tax code is quick and free through your HMRC Personal Tax Account. You can view your current code, see how it was calculated, and compare it to your payslip.
How to Fix a Wrong Tax Code
If you find an error, you do not need to call HMRC in most cases. You can fix it through your Personal Tax Account.
Step 1: Report the change
In your Personal Tax Account, look for the option to Check your Income Tax estimate or Tell us about a change. Click on it.
This is where you can tell HMRC about anything that has changed. The most common things to report are:
- Starting or stopping a job
- Changes to benefits in kind such as a company car or medical insurance
- Changes to your expected income
- Marriage Allowance changes
- Changes to your personal details
Step 2: Wait for HMRC to respond
After you report a change, HMRC will review your information. If a new tax code is needed, they will issue one. You will receive a P2 coding notice confirming the change.
Step 3: Check your next payslip
Your employer will be notified automatically. The new code should appear on your next payslip, usually within one or two pay periods. If it does not, contact your payroll department.
If you have reported changes and your code is still wrong, you can contact HMRC directly by phone on 0300 200 3300 or through your Personal Tax Account.
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.
What to Do If You Have Overpaid or Underpaid
Once your tax code is corrected, any overpayment is usually refunded automatically through your next payslip. Your employer adjusts the deduction so you get the money back.
If the overpayment is large, HMRC may refund it directly to your bank account instead of through payroll. This is more likely to happen at the end of the tax year when HMRC issues a P800 tax calculation.
If you have underpaid tax, HMRC will adjust your tax code to collect the balance. They will usually spread the collection over the remaining months of the tax year so it does not cause too much strain on your monthly budget.
Use our Income Tax Calculator to confirm you are paying the right amount after the correction.
For more on claiming refunds, our step-by-step tax refund guide explains the process in full.
Once corrected, overpaid tax is usually refunded through your payslip. If you have underpaid, HMRC will adjust future tax. Check your payslip after the correction to confirm it is right.
How to Avoid Tax Code Problems in Future
Preventing tax code errors is easier than fixing them. A few simple habits can save you a lot of trouble.
Always give your P45 to a new employer. This is one of the most important things you can do. Without a P45, your employer may need to use temporary information until HMRC provides updated details. If you have lost your P45, complete the starter checklist when you start your new job.
Check your payslip every month. Your tax code is printed on every payslip. If it changes unexpectedly, check your Personal Tax Account to understand why. Do not assume HMRC has got it right.
Tell HMRC when things change. If you start receiving benefits, change jobs, or your income changes significantly, report it through your Personal Tax Account. Do not wait for HMRC to update your records themselves.
Review your P60 at the end of the tax year. Your P60 shows your total pay and tax for the year. Compare it to your own records and make sure everything adds up.
Our why HMRC changes tax codes mid-year guide explains the common triggers for code changes.
Providing your P45 to new employers, checking your payslip regularly, and updating HMRC when your circumstances change can help you avoid future tax code errors.
Final Thoughts
Your tax code is not something you should ignore. A small error can cost you hundreds of pounds a year. Checking it online takes a few minutes and could save you a significant amount of money.
If you find an error, fix it through your Personal Tax Account. If you have overpaid, claim your refund. If you have underpaid, arrange to pay what you owe before it becomes a problem.
Check your tax code regularly, especially after starting a new job or receiving new benefits. It is one of the simplest financial checks you can do, and it is completely free.
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