Introduction – Are You Paying Too Much Tax Because of a Wrong Tax Code?
Do you know thousands of UK taxpayers overpay taxes every year simply because they are on the wrong tax code? Many remain unaware that they can claim their overpayment after changing their tax code.
The reason for a wrong tax code is that HMRC uses incorrect or outdated information about your income, benefits, or personal circumstances. The good news is that you can change your tax code anytime via the HMRC online portal quickly and easily.
Under the UK PAYE system, your employer deducts Income Tax, but they do not determine your tax code. That responsibility lies solely with HMRC.
Correcting a wrong tax code is straightforward. A new code is usually issued to your employer within one to two pay periods. For 2026/27, the standard Personal Allowance remains £12,570.
At Hussain Associates, we help employed, self-employed, and multi-income individuals get the correct tax code. We save your valuable time and money.
What Is a Tax Code and Why Does It Matter?
Your tax code is simply a set of numbers and letters from HMRC. It tells your employer or pension provider how much Income Tax to take from your pay under PAYE.
The numbers show your tax-free income for the year. So 1257L means you can earn £12,570 tax-free in 2026/27. The letter explains your situation, like whether you get the standard Personal Allowance or have adjustments for benefits or underpaid tax.
So why should you care? Even a tiny mistake can cost you hundreds in overpaid tax each year. A wrong code means your employer takes too much or too little from your pay.
Your tax code shifts when life changes. Starting a new job, getting a company car, marrying, or drawing a pension can all trigger a change. HMRC sends a P2 coding notice whenever your code updates. A quick check of your tax code could save you a fortune.
How to Check Your Current Tax Code (Before Making Any Changes)
Before you can change your tax code, you need to know what it is and whether it is correct. Checking your tax code regularly could save you hundreds of pounds in overpaid tax.
There are several ways to check your current tax code:
Check Your Payslip
Your tax code appears on every weekly or monthly payslip, usually near your National Insurance number. If you are unsure, your Payroll team can confirm your current code.
Check Your P60 or P45
Your P60 is issued at the end of each tax year and shows your tax code. If you are leaving a job, your P45 will also display your tax code.
Check Online via the HMRC Website
Visit the HMRC official website and sign in to your Personal Tax Account. You need your Government Gateway ID and National Insurance number. If you do not have an account, you can create one using your email.
Use the HMRC Mobile App
You can also download the HMRC mobile app to check your tax code anytime, anywhere, directly from your phone.
Once you have checked your tax code, compare it with your circumstances. Is your income correct? Are all your benefits listed? If anything is wrong, you can change your tax code by updating your details with HMRC.
Step-by-Step Guide – How to Change Your Tax Code
A wrong tax code doesn’t mean you’re stuck. You can ask HMRC to update it.
Step 1: Check Your Current Tax Code: Your payslip, P60, or P45 shows your current tax code. You can also use the HMRC mobile app or your Personal Tax Account.
Step 2: Identify the Problem: Sign in with your Government Gateway ID and check your dashboard. Find what’s incorrect. You might have the standard 1257L code, but HMRC put you on an emergency code like 1257L X.
Step 3: Update Your Details: Go to Income Tax, select PAYE, choose your employment, and update your job details. If you qualify for Marriage Allowance or Uniform Tax Relief, tell HMRC. They’ll send your new code to your employer.
Step 4: Contact HMRC If Needed: Can’t update online? Call HMRC or use web chat. Keep your National Insurance number, payslip details, and estimated income ready.
Step 5: Wait for the New Code: HMRC issues a new code within 15 days online. Started a new job? Wait 35 days for HMRC to get your income details. Your new code will appear on your next payslip.
Common Reasons Why Tax Codes Change (And When You Should Check Yours)
Your tax code changes with your situation. Common reasons include:
Change Job: If you start a new job, leave a job, or earn from a second job, your tax code may change. Your Personal Allowance may be split between multiple employers.
Personal Allowance Adjustments: If your tax-free Personal Allowance is adjusted, your tax code changes. This happens if your income exceeds £100,000 or if you transfer allowance to your spouse.
Benefits or Deductions: Company benefits like a car, medical insurance, or accommodation reduce your Personal Allowance. If your car benefit ends, your taxable benefit reduces, affecting your tax code.
Marriage Allowance: Your tax code changes if you get married, divorced, or enter a civil partnership. You can transfer up to £1,260 of your Personal Allowance to your spouse.
Start Receiving a Pension: You need to adjust your tax code if you start receiving a state or private pension.
Underpayment or Overpayment: If you owe tax from a previous year, HMRC may reduce your tax-free allowance through a K code. If you overpay, you can change your code to claim a refund.
Uniform Tax Relief: If you pay for work-related expenses, you may be eligible for tax relief, which affects your tax code.
Understanding UK Tax Codes – A Quick Reference Table
Tax codes can be confusing, but understanding them is essential to avoid overpaying taxes. Each code tells you and your employer how much tax-free income you are entitled to. Below is a quick reference table explaining the most common UK tax codes.
| Tax Code | Situation | Applies To | How Tax Is Calculated |
| 1257L | Standard Personal Allowance | One Job | Tax paid after £12,570 |
| 1257L W1/M1/X | Emergency Tax Code | New job without details | Only for the current period |
| BR | Basic Rate (20%) | Second job or pension | All income is taxed at 20% |
| D0 | Higher Rate (40%) | Higher-rate taxpayers with extra income | All income is taxed at 40% |
| D1 | Additional Rate (45%) | Additional-rate taxpayers | All income is taxed at 45% |
| NT | No Tax | Special cases | No tax deducted |
| K Code (e.g., K250) | You owe tax or have benefits | Company car, medical allowances, etc. | Extra tax deducted |
| M | Marriage Allowance received | Lower-earning spouse | Higher tax-free allowance |
| N | Marriage Allowance transferred | Higher-earning spouse | Lower tax-free allowance |
| T | Adjusted allowance | Income over £100k or complex tax | Allowance reviewed by HMRC |
| S | Scottish tax code | Scottish taxpayers | Scottish Income Tax rates apply |
| C | Welsh tax code | Welsh taxpayers | Welsh Income Tax rates apply |
Welsh Income Tax rates apply
If your tax code does not match your circumstances, you may be on the wrong tax code and overpaying taxes. Check your code against this table and contact HMRC if anything seems incorrect.
Common Tax Code Mistakes That Cost You Money (And How to Avoid Them)
Many taxpayers overpay taxes due to simple mistakes. Here are common errors and how to avoid them:
Ignoring emergency tax codes – Emergency codes like 1257L W1/M1/X mean you are taxed only on your current pay period. Contact HMRC immediately.
Not checking after changing jobs – Your tax code is not automatically updated. Always check your first payslip at a new job.
Forgetting to inform HMRC about a second job – Your second job may be put on a BR code, meaning all income is taxed at 20%. Inform HMRC.
Overlooking taxable benefits – Benefits like company cars reduce your Personal Allowance. Update HMRC if benefits change.
Not updating estimated income – If your income changes, update your estimate with HMRC.
Ignoring taxable allowances exceeding Personal Allowance – Review your total income annually.
Not checking tax code each tax year – Always check your code at the start of each new tax year.
Overlooking tax code notice P2 – HMRC sends a P2 notice whenever your tax code changes. Always read it.
What Happens After HMRC Issues a New Tax Code? (Employer Notifications and Payroll Updates)
Once HMRC agrees your tax code is incorrect, they issue an updated coding notice and send the new code to your employer or pension provider. You do not need to contact your employer.
Your employer receives the new code through HMRC’s PAYE system and must apply it to your payroll. You should see the new code on your next payslip, usually within one to two pay periods.
If your employer uses payroll software, the update is applied without delay. If your tax code has not changed after two pay periods, contact HMRC to confirm the new code and ask your employer to check their PAYE notifications.
HMRC also sends you a P2 coding notice explaining your new tax code. Read this notice to confirm all details are correct. If you opted for paperless updates, you will receive this notice online.
Can You Claim a Refund If You’ve Already Overpaid Tax?
If you have overpaid tax due to a wrong tax code, you can claim a refund from HMRC. The process is straightforward.
How to Claim
Log in to your HMRC Personal Tax Account, check your tax code history, and HMRC will calculate any overpayment. If you are due a refund, they will send it via bank transfer or cheque.
You can also claim by contacting HMRC by phone or web chat. Have your National Insurance number and employment details ready.
For previous tax years, you can claim overpayments going back up to four years.
What to Expect
Once HMRC confirms your overpayment, they usually issue the refund within 4 to 6 weeks. If you are still employed, HMRC may adjust your tax code to refund you through your pay.
If you are unsure how to claim, Hussain Associates can help you check your tax history, calculate your overpayment, and handle your claim with HMRC.
Final Thoughts: Check and Change Your Tax Code Before You Overpay
Your tax code determines how much tax you pay. Even a small error can cost you hundreds of pounds each year. Many taxpayers never check their tax code and overpay without realising.
Changing your tax code is quick and simple. Check your code online, update your details with HMRC, and your employer will receive a new code within one to two pay periods. By following this guide, you can stop overpaying and keep more of your money.
Check your tax code regularly, especially after starting a new job, receiving benefits, or life changes like marriage. Always read your P2 coding notice and act if something seems incorrect.
If you are unsure about your tax code or need help claiming a refund, Hussain Associates is here to help. Our experts review your tax position, identify errors, and handle claims with HMRC. We save you time, money, and the hassle of complex tax issues.
Take control of your tax affairs today. Check your tax code and ensure you are paying the right amount.
