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Tax Codes

When you start a new job or your pay changes, one of the first things you’ll see on your payslip is a tax code. It looks like a mix of numbers and letters (for example, 1257L), and it decides how much Income Tax you pay.

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This guide breaks down what a tax code is, how it’s worked out, and what to do if it looks wrong.

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1. What Is a Tax Code?

Your tax code is a short code used by HMRC to tell your employer:

  • How much of your income should be tax-free

  • How much Income Tax to take from your pay

 

Your employer uses this code every time they pay you, through the PAYE (Pay As You Earn) system.

 

If your tax code is wrong, you could pay too much or too little tax.

 

2. The Standard Tax Code (1257L)

For many people in the UK, the standard tax code is currently 1257L.

  • The number (1257) shows how much of your income is tax-free in a year:

    • 1257 → £12,570 tax-free allowance

  • The letter (L) means you’re entitled to the basic Personal Allowance.

 

If you have this code and only one job, you’re usually being taxed in the standard way.

 

3. How Tax Codes Are Worked Out

HMRC looks at your situation and decides your code based on things like:

  • Your Personal Allowance

  • Any benefits from your employer (for example, a company car)

  • Any untaxed income (for example, rental income)

  • Whether you have more than one job or pension

  • Whether you owe tax from a previous year

 

They then turn this into a code that tells your employer how much of your income should be tax-free.

 

4. What the Numbers Mean

The number part of your tax code is usually:

 

Your tax-free amount ÷ 10

Examples:

  • 1257L → £12,570 tax-free

  • 1100L → £11,000 tax-free

  • 0T → No tax-free allowance given in the code

 

If your tax-free amount is reduced (for example, because of benefits or unpaid tax), the number will be lower.

 

5. What the Letters Mean

The letter in your tax code gives extra information. Some common ones:

  • L – You get the standard Personal Allowance.

  • M – You’ve received part of your partner’s Personal Allowance (Marriage Allowance).

  • N – You’ve transferred part of your Personal Allowance to your partner.

  • T – HMRC needs to review your situation (for example, complex allowances).

  • BR – All your income from this job is taxed at the basic rate (no Personal Allowance used here).

  • D0 / D1 – All income from this job is taxed at higher or additional rate.

  • K – You have more deductions than allowances (for example, benefits or unpaid tax are higher than your tax-free amount).

 

If you see a letter you don’t recognise, it’s worth checking what it means.

 

6. Emergency and Temporary Tax Codes

Sometimes HMRC doesn’t yet have full information about you (for example, when you start a new job). In that case, you might get an emergency tax code.

 

You might see:

  • 1257L W1, 1257L M1, or 1257L X

    • W1 = Week 1 basis

    • M1 = Month 1 basis

 

This means your tax is worked out only on that week or month, not the whole tax year. It’s a temporary way to avoid big over- or under-payments while HMRC catches up.

 

Once HMRC has the right details, they’ll update your code and your tax should correct itself over time.

 

7. Where to Find Your Tax Code

You can usually find your tax code on:

  • Your payslip

  • Your P45 (when you leave a job)

  • Your P60 (end-of-year summary)

  • Your Personal Tax Account on the HMRC website

 

On a payslip, it’s often near your name or National Insurance number.

 

8. When Your Tax Code Might Change

Your tax code can change during the year if:

  • You start or leave a job

  • Your income goes up or down

  • You start receiving a company benefit (like a car or medical insurance)

  • You claim or stop claiming Marriage Allowance

  • HMRC corrects tax you underpaid or overpaid in a previous year

 

When this happens, HMRC usually sends you a tax code notice (by post or online).

 

9. How to Check If Your Tax Code Is Right

Ask yourself:

  • Do you have more than one job or pension?

  • Do you receive benefits from your employer?

  • Have you recently changed jobs?

  • Does your code match what HMRC has told you?

 

If something doesn’t feel right:

  1. Compare the code on your payslip with the one in your HMRC account or letter.

  2. Read the explanation in your tax code notice (if you have one).

  3. Use HMRC’s online tools or contact them to ask for a review.

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10. What to Do If You Think Your Tax Code Is Wrong

If you think your tax code is incorrect:

  1. Contact HMRC – Give them details of your jobs, income and benefits.

  2. Keep your payslips – They help show what tax you’ve already paid.

  3. Watch for a new code – HMRC may send a new code to you and your employer.

  4. Check future payslips – Make sure the new code has been applied.

 

If you’ve overpaid tax, HMRC will usually refund you (through your pay or directly). If you’ve underpaid, they may collect it through a future tax code or ask for payment.

11. Why Understanding Your Tax Code Matters

Knowing your tax code helps you:

  • Check you’re paying the right amount of tax

  • Spot mistakes early

  • Understand changes in your take-home pay

  • Plan your budget with more confidence

 

Your tax code is small, but it has a big impact on your pay. Taking a few minutes to understand it is a key step towards becoming truly tax-savvy.

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