UK Tax Code Explained: What Every Letter Means (2026)

Frozen until 2031: The Autumn 2025 Budget extended the freeze on the £12,570 Personal Allowance by another three years, to April 2031. 2026/27 is the sixth straight year of frozen thresholds — which means more people are being pulled into higher tax bands by pay rises alone, and more tax codes are quietly going wrong.At a glance

• Your tax code tells your employer or pension provider how much tax-free income to give you. It is not a statement that HMRC has checked your affairs.
• The number is your tax-free allowance with the last digit removed. 1257L means £12,570 tax free — the standard code for 2026/27.
• The letters describe your situation: L standard, M/N marriage allowance, BR/D0/D1 flat rates on a second income, K means untaxed income exceeds your allowance.
• An S prefix means Scottish rates; a C prefix means Welsh rates. Scotland has six bands in 2026/27, from 19% to 48%.
• W1, M1 or X on the end means you are on an emergency code and are very likely overpaying.
• Not financial or tax advice: This article explains the rules in plain English. For your specific situation, speak to an accountant, HMRC, or Citizens Advice.

Most people have never chosen their tax code. It simply appears — on a payslip, on a P45, on a letter from HMRC with a reference number and very little explanation. And because it looks like an internal code rather than a decision about your money, most people never question it.

That is a costly habit. Your tax code is the single instruction that decides how much income tax comes out of your pay each month. Get it wrong and you either hand HMRC money you did not owe, or quietly build up a bill you will be asked to settle later.

Tax codes go wrong more often than people assume: after a job change, when a second job starts, when a benefit like a company car is added, or when HMRC estimates something it cannot see. Here is how to read yours in about five minutes.

What the number actually means

The number in your tax code is your annual tax-free allowance with the final digit knocked off. So 1257 stands for £12,570 — the standard Personal Allowance, unchanged since 2021/22 and now frozen until April 2031.

That allowance is spread across the year: roughly £1,047 tax free each month, or £241 a week. Anything above that is taxed at your marginal rate. If your number is lower than 1257, something is reducing your allowance. Neither a lower nor a higher number is automatically wrong — but both are worth understanding.

Why your number might be lower than 1257

• A taxable benefit — a company car, fuel, or private medical insurance. HMRC collects the tax on these by shrinking your allowance rather than sending you a bill.
• Underpaid tax from an earlier year being collected gradually through your pay.
• Untaxed income HMRC knows about, such as savings interest above your Personal Savings Allowance or modest rental income.
• Income over £100,000 — your allowance drops by £1 for every £2 above that line, and disappears entirely at £125,140.

What the letters mean

The letter is the part people find most baffling, but there are only a handful that matter.

• L — you get the standard Personal Allowance. The most common code by far.
• M — you have received 10% of your partner's allowance under Marriage Allowance.
• N — you have given away 10% of your allowance to your partner.
• T — your code contains items HMRC needs to review, often because income is near £100,000.
• 0T — no tax-free allowance at all. Usually means HMRC has no details for you yet, or your allowance is fully used elsewhere.
• BR — all income from this job is taxed at basic rate (20%), with no allowance. Normal for a genuine second job, wrong if it is your only one.
• D0 — all income taxed at higher rate. D1 — additional rate. D2 exists in Scotland for the top rate.
• NT — no tax deducted at all. Rare, and usually deliberate.
• K — see below. This one behaves differently from all the others.

The K code, explained properly

A K code appears when the things reducing your allowance are worth more than the allowance itself. Instead of tax-free income, you have notional extra income added to your pay for tax purposes.

So K500 means roughly £5,000 is added to your taxable pay across the year. K codes commonly follow a large company car benefit or a sizeable underpayment being recovered.

There is one protection worth knowing: a K code can never take more than 50% of your gross pay in tax in any pay period. If it would, the excess rolls forward instead.

Not sure what your coding notice is telling you? Upload your P2 coding notice, payslip or P60 to Clarify and ask in plain English — "why has my allowance gone down?" or "what is this K code doing to my pay?". You get an answer that points back to the exact lines in your own document, not generic guidance about someone else's situation.

Try Clarify free → getclarify.co.uk

Prefixes: S and C

An S at the front — as in S1257L — means you are a Scottish taxpayer and Scottish rates apply. For 2026/27 Scotland has six bands: starter 19%, basic 20%, intermediate 21%, higher 42%, advanced 45% and top 48%. The Personal Allowance itself is still £12,570, because that part is set by Westminster.

A C at the front means Welsh rates, which currently match those in England and Northern Ireland. Your prefix follows where you live, not where you work — so if you moved across the border and never told HMRC, your code may be wrong.

Emergency codes: W1, M1 and X

If your code ends in W1, M1 or X, it is being applied on a "non-cumulative" basis. Your employer taxes each pay packet in isolation, ignoring what you have already earned and paid this tax year.

It usually follows starting a new job without a P45, and is meant to be temporary. Left alone, it often means overpaying — particularly if you had a gap between jobs, because you never get the benefit of the unused allowance from those weeks.

How to check your code in ten minutes

1. Find the code. It is on your payslip, your P60, your P45, and on any P2 "Tax Code Notice" letter from HMRC.
2. Check the number. If it is not 1257, work out what is reducing or increasing it. Your P2 notice itemises this line by line.
3. Check the letter. BR or 0T on your only job is a red flag. So is an M or N if you have never applied for Marriage Allowance.
4. Check the prefix. Does S or C match where you actually live?
5. Check for W1/M1/X. If present, chase it — this is the most common cause of quiet overpayment.
6. Compare against reality. Do the listed benefits still exist? People routinely carry a company car deduction for a year after giving the car back.

What to do if it looks wrong

Contact HMRC directly — through your Personal Tax Account online, or by phone. Your employer cannot change your code; they are legally required to apply whatever HMRC sends them.

Have your National Insurance number, your latest payslip, and the P2 notice to hand. Explain what has changed rather than simply saying the code is wrong: "I returned my company car in March" gets a faster fix than "my tax seems high".

If you have overpaid, HMRC usually corrects it within the same tax year through an adjusted code, so the money comes back through your pay. If the year has closed, you can reclaim for the previous four tax years. If you have underpaid, ask about spreading the recovery over a longer period — that is often possible, and far less painful than a single deduction.

Stop filing tax letters unread. Coding notices, P60s, P800 calculations and HMRC reminders all use language designed for payroll systems, not people. Clarify reads your document and answers your actual question — with citations back to the page it came from, so you can check the answer rather than take it on trust.

Decode your tax letter now → getclarify.co.uk

Frequently asked questions

Is 1257L the right code for me?

It is right if you have one job or pension, earn under £100,000, claim no Marriage Allowance, and receive no taxable benefits. If any of those do not apply, a different code may be entirely correct.

Why did my tax code change mid-year?

HMRC updates codes whenever new information arrives — a benefit reported by your employer, a change in estimated savings interest, or an underpayment identified from a previous year. You should receive a P2 notice explaining it.

My second job is on BR. Is that a mistake?

Usually not. Your allowance is normally attached to your main job, so the second one is taxed at basic rate from the first pound. If your main job pays less than your allowance, though, you may be able to split the allowance across both.

What does 0T mean and why do I have it?

0T gives no tax-free allowance. It typically appears when a new employer has no P45 and no starter checklist from you, or when your allowance is already fully allocated elsewhere. Sending your employer a completed starter checklist usually resolves it.

Can my employer change my tax code for me?

No. Employers must apply the code HMRC issues. Any correction has to come from HMRC, though your employer may need to report a change — such as removing a benefit — before HMRC can act.

How do I get overpaid tax back?

Within the current tax year, HMRC normally issues a corrected code and the refund arrives through your pay. For closed years, HMRC often sends a P800 calculation automatically, but you can claim back up to four tax years yourself.

Does a K code mean I have done something wrong?

No. It simply means the value of your taxable benefits or adjustments exceeds your Personal Allowance. It is common among people with substantial company cars, and among those repaying an earlier underpayment.

I moved to Scotland — will my code update automatically?

Only if HMRC has your current address. The S prefix is applied based on the address HMRC holds, so update it through your Personal Tax Account as soon as you move. Otherwise you may be taxed under the wrong regime for months.

Related articles

• UK Payslip Explained: What Every Line Means (2026)
• Decoding HMRC Letters: Every Reference Code and What to Do Next
• Self-Assessment Jargon Decoded: A Plain-English Guide
• What Your Pension Statement Actually Means

This article is general information only and is not legal, tax or financial advice. Tax rules change and individual circumstances vary. For advice on your own situation, contact HMRC, a qualified accountant, or Citizens Advice.