How Tax Codes Work and What Yours Means

Your tax code determines exactly how much income tax HMRC expects your employer to deduct from your salary each month. It's the four characters on your payslip that control the gap between your gross pay and take-home — yet most people never check if it's actually correct. This guide explains how tax codes work and what yours means, so you can spot errors and keep more of your money.

What Is a Tax Code and How Does It Work?

A tax code is HMRC's instruction to your employer on how much tax to deduct. It combines two pieces of information: how much of your income is tax-free (your personal allowance) and any adjustments for your specific circumstances (pension, benefits, second job, etc.).

The standard tax code for most people in 2026 is 1257L. Here's what that means:

The number (1257) represents your personal allowance divided by 10. So 1257 × 10 = £12,570 — exactly the personal allowance for this tax year.
The letter (L) indicates you're eligible for the basic personal allowance with no special circumstances.

But there are other letters:

L — standard personal allowance. Most people.
M — transferred allowance from a partner (married couple's allowance).
N — you've transferred your allowance to a partner (yours is lower).
T — HMRC is checking your tax situation. You're still taxed correctly, but they may owe you a refund once they've finished reviewing.
K — your allowance is exhausted. You have other taxable income (rental, benefits in kind, multiple jobs) that requires a different calculation.

If you see a code like 0T or BR on your payslip, HMRC is using an emergency code — this usually happens when you start a second job or they're reviewing your situation. It's not a problem, just temporary.

How to Read Your Tax Code and Understand Your Deductions

Let's decode real examples.

1257L (the standard)

You have a £12,570 personal allowance.
On a £35,000 salary, you owe tax on £22,430 (£35,000 − £12,570).
That's £4,486 in income tax at 20%, plus £1,794 in National Insurance (8% on earnings above £12,570).
Take-home: £27,824 (before pension or student loans).

1100L (reduced allowance)

Your allowance is lower than standard — perhaps you have a second job or previous underpayment.
1100 × 10 = £11,000 of tax-free income.
The gap: £12,570 − £11,000 = £1,570 of extra taxable income.
On that same £35,000 salary, you'd owe £4,800 in income tax (£314 more).
Take-home: £27,406 (£418 less per year).

500K (allowance exhausted)

Your allowance is used up. HMRC wants to collect tax on the first £5,000 of your income (500 × 10).
This usually means you have untaxed income like benefits in kind or rental income.
You'll pay tax on every pound up to £5,000, then normal rates apply.

0T (emergency code)

HMRC has temporarily removed your allowance while they investigate or you've just started a second job.
You're taxed at 20% on every pound until they issue a permanent code.
Don't worry — the refund is coming. Contact HMRC to speed it up.

That £418 difference between 1257L and 1100L is why it matters. A wrong tax code costs real money. If you're comparing take-home pay across job offers, your tax code can swing the figure by hundreds of pounds per year.

Why Your Tax Code Changes

HMRC updates your code when your circumstances change:

New job or second job: HMRC has to split your allowance between employers. Your main job gets most of it; your second job may get code BR (basic rate, taxed at 20% on all income).
Pension contributions: Workplace pension contributions reduce your taxable income automatically. HMRC's code reflects this — it's tax relief built in.
Salary sacrifice schemes: Cycle-to-work, childcare vouchers, or electric car salary exchange reduce your gross pay, so your code adjusts downward (lower taxable income = lower code).
Benefits in kind: A company car, accommodation, or health insurance has a taxable value. HMRC adds this to your code as extra tax to collect.
Previous year's underpayment or overpayment: If you owed tax in 2024–25 or are due a refund, HMRC collects or refunds it by adjusting your 2025–26 code.
Rental income or investments: Untaxed income triggers a K code or adjustment so HMRC collects tax via PAYE rather than waiting for Self-Assessment.

These changes are automatic — HMRC keeps your tax right throughout the year. But if your code changes unexpectedly, the letter that came with it will explain why. If you're unsure, check HMRC's online tax account or your P60 (annual statement).

How to Check and Update Your Tax Code

If you think your code is wrong:

Find your code — it's on your payslip, P60, or in your HMRC online tax account.
Check HMRC's records — log into HMRC's Personal Tax Account. You'll see what they think your allowance is and why.
Spot the error — common mistakes include a second job that wasn't registered, a pension change that wasn't applied, or HMRC collecting an old debt.
Update it — use your HMRC account or call them. Changes take effect within a few weeks.
Claim a refund — if you've been over-taxed, HMRC settles via P800 (usually in April after the tax year ends) or sooner if you contact them.

If you're changing jobs, your new payslip may show an unusual code because your previous employer was still withholding tax. Your old employer's P45 explains any underpayment. Your new employer will adjust it in the first week or month.

How Pension and Benefits Affect Your Code

If you contribute to a workplace pension, HMRC doesn't charge you income tax on that contribution — it's automatic. Your code reflects it: your taxable income is simply lower because the contribution is taken before HMRC's calculation. This is pension tax relief in action.

If you have a company car or other benefit in kind, HMRC adds a taxable value to your code. A mid-range electric car might be valued at £2,000/year in taxable benefit. Your code increases by 200 (since the code is divided by 10), so you'd see 1457L instead of 1257L.

If you do a salary sacrifice scheme, your gross salary decreases — and so does your tax and National Insurance. Your code adjusts automatically because your taxable income is lower.

Frequently Asked Questions

Q: What if my tax code is wrong? Will I get a refund? A: Yes. HMRC calculates your tax based on your code and the income you actually earn. If your code is wrong, you're either over-taxed or under-taxed. HMRC settles the difference via P800 (usually in April after the tax year ends). Over-taxation refunds are paid to your bank account; under-taxation is usually collected via your code for the next year.

Q: Why do I have code 0T on my payslip? A: Code 0T means HMRC has temporarily removed your personal allowance while they investigate or you've just started a second job. You're still taxed correctly — your code will go back to normal once HMRC finishes their check. In the meantime, you're taxed at 20% on every pound, but the refund is coming.

Q: Does my tax code change if I get a pay rise? A: No. A pay rise doesn't change your code. You just pay more tax on the extra income because of your tax bracket. Work out exactly how much your take-home will increase using our salary calculator.

Q: What if I have two jobs? What tax codes apply? A: HMRC splits your £12,570 allowance between your jobs. Your main job gets most of it; your second job gets code BR (basic rate, taxed at 20% on all income) or 0T. Update HMRC's records with both employers to rebalance the codes.

Q: When should I contact HMRC about my code? A: Contact them immediately if your code doesn't match your circumstances (second job, pension change, address move, benefits in kind). You can update online via HMRC's tax account in minutes. Changes take effect within a few weeks.

Q: Can I calculate my take-home if I know my tax code? A: Yes. Multiply your code number by 10 to get your tax-free allowance. Subtract that from your gross salary; the remainder is taxable at 20% (basic rate) unless it goes above £50,270 (then 40% applies). Our UK salary calculator does all this automatically — just enter your code, salary, and any deductions.

Calculate Your Exact Take-Home Pay

Your tax code is only accurate if it delivers your correct tax bill every month. The only way to verify you're keeping the right amount is to calculate your full take-home — including National Insurance, pension contributions, and any other deductions.

Use our UK salary calculator to model your exact situation. Enter your gross salary, tax code, pension contribution percentage, and any other deductions. In seconds, you'll see your income tax, National Insurance, monthly and annual take-home, and a breakdown of every deduction.

If you're evaluating a job offer or a pay rise, run both scenarios through the calculator. The highest gross salary doesn't always mean the highest take-home — location, tax code, and benefits matter more than you'd think.