Your Tax Code Explained — What the Letters and Numbers Mean for Trade Business Owners (2026)

What a Tax Code Actually Is

A tax code is a short combination of numbers and letters that HMRC issues to your employer or pension provider. Its job is simple: it tells them how much Income Tax to deduct from your pay or pension before it reaches you. The code is applied through PAYE (Pay As You Earn), the system HMRC uses to collect tax on employment and pension income at source.

The key point for tradespeople is that a tax code only governs PAYE income. It has nothing to do with the profits of a sole trader or partnership, which are taxed through Self Assessment. But the moment you take a salary through your own limited company, or you have an employed job alongside your trade, a tax code is in play — and it's your responsibility to make sure it's right.

Why Your Tax Code Matters as a Tradesperson

Tax codes are easy to ignore until they cost you money. They matter most in three common situations for people in the trades:

• You're a limited company director paying yourself a salary through PAYE. Your company runs a payroll, applies your tax code and deducts tax (and National Insurance) from your director's salary. The wrong code here means your company is deducting the wrong amount every payday.
• You have a PAYE job alongside a self-employed side trade. Your employed wage runs through PAYE with a tax code, while your trade profits are taxed separately through Self Assessment. Splitting your personal allowance across two income streams is where codes most often go wrong.
• You're an employee thinking about going self-employed. Understanding how your current code uses up your personal allowance helps you plan the switch and avoid nasty surprises in your first Self Assessment.

The Numbers: What 1257L Means

The most common tax code in the UK is 1257L. Break it into two parts and it's easy to read.

The number represents your tax-free Personal Allowance — the amount you can earn before paying any Income Tax. For 2025/26 the standard Personal Allowance is £12,570. HMRC takes that figure, drops the last digit, and that's your code number: £12,570 ÷ 10 = 1257. So the number is simply your allowance divided by ten.

The letter describes your situation. The L in 1257L means you're entitled to the standard tax-free Personal Allowance. Put together, 1257L tells your employer: give this person £12,570 of tax-free pay across the year, spread evenly across each pay period, and tax everything above it at the normal rates.

The Letters: What Each One Means

The number tells your employer how much tax-free pay to give you; the letter explains why, or flags a special rule. These are the letters you're most likely to come across.

L — Standard Personal Allowance

You get the standard tax-free Personal Allowance. This is the default for most employees and most director-shareholders taking a normal salary.

M and N — Marriage Allowance

These relate to the Marriage Allowance, which lets one spouse or civil partner transfer 10% of their Personal Allowance to the other. M means you've received 10% of your partner's allowance (so your code number goes up). N means you've transferred 10% of your allowance to your partner (so your code number goes down). Worth knowing if one of you has lower income from the trade than the other.

BR — Basic Rate on Everything

All income from this source is taxed at the basic rate of 20%, with no Personal Allowance applied. BR is extremely common on a second job or second income, because your tax-free allowance is already being used up against your main job. If you have an employed job and your company also pays you a salary, expect one of them to sit on BR.

D0 — Higher Rate on Everything

All income from this source is taxed at the higher rate of 40%, with no allowance. You might see D0 on a secondary income when your main income already fills the basic-rate band.

D1 — Additional Rate on Everything

All income from this source is taxed at the additional rate of 45%. This appears for higher earners whose other income already uses up the higher-rate band.

0T — No Allowance

The zero means no Personal Allowance is applied, and income is taxed across the normal bands (20%, 40%, 45%) from the first pound. 0T is often used when you start a job without a P45 and haven't completed a starter checklist, or where your allowance is already fully used elsewhere. New director payrolls frequently start here by mistake.

NT — No Tax

No tax is taken from this income at all. It's rare and applies in specific circumstances, such as certain non-resident situations.

K Codes — Deductions That Exceed Your Allowance

A code starting with K works in reverse. Normally your allowance is subtracted from your pay before tax. A K code is used when deductions — such as taxable company benefits (a van or fuel benefit, medical cover) or tax owed from a previous year — are greater than your tax-free allowance. Instead of being taken away, the extra amount is added to your taxable income, so you pay tax on more than you actually earn from that job. There's a safeguard: a K code can never take more than 50% of your gross pay in a single pay period.

Emergency Tax Codes (W1, M1 and X)

If you see W1, M1 or X attached to your code (for example 1257L W1), you're on an emergency, or non-cumulative, code. W1 means week 1, M1 means month 1, and X is used more generally.

Normally tax codes are cumulative: each payday looks at your total pay and tax for the year so far and balances things out. A non-cumulative code ignores everything before the current pay period and just taxes that period in isolation. It's a temporary measure HMRC uses when it doesn't yet have your full picture — typically after starting a new job without a P45. It can cause you to overpay or underpay until HMRC issues a proper cumulative code, so it's worth chasing.

High Earners: How the Allowance Tapers Away

If your income is high — which can happen when you combine a director's salary, dividends and other income — your Personal Allowance starts to disappear. For every £2 of income above £100,000, you lose £1 of allowance. By the time income reaches £125,140, the Personal Allowance is gone entirely.

HMRC reflects this by reducing your tax code number, and in some cases switching you to a K code. The taper creates an effective marginal tax rate of around 60% on the slice of income between £100,000 and £125,140, which is why higher-earning trade business owners often plan salary and pension contributions carefully around that band.

Why Directors and Multiple-Income Tradespeople Get the Wrong Code

Tax codes assume HMRC has a clear, up-to-date view of your income. Tradespeople frequently break that assumption:

• New limited company payrolls. When you first run payroll for your own company, the code can default to 0T or an emergency code until HMRC catches up, meaning you overpay early on.
• Two income sources. With an employed job and a company salary (or two employments), your single Personal Allowance has to be allocated to one source. If HMRC splits it badly, you can end up with the wrong deductions on both.
• Company benefits. A company van, fuel or private medical cover is a taxable benefit reported on a P11D. HMRC adjusts your code to collect the tax — and if the benefit details are out of date, the code is wrong.
• Estimated investment or dividend income. HMRC sometimes adjusts your code to collect tax on estimated dividends or savings. If the estimate is off, so is your code.

How to Check and Correct Your Tax Code

Your current code appears on your payslip, your P45 when you leave a job, your P60 at the end of the tax year, and on any PAYE Coding Notice (form P2) HMRC sends you. The quickest way to see and manage it is your Personal Tax Account on GOV.UK.

• Sign in to your Personal Tax Account and open the "Check your Income Tax" section.
• Review how HMRC has worked out your code — the allowances it's given and the deductions it's made.
• Update anything that's wrong online — for example a company benefit you no longer have, or an estimated income figure that's out of date.
• If it's not something you can fix online, contact HMRC directly to ask them to reissue the code.

When HMRC changes your code, they issue a new one to your employer or pension provider, who then apply it from the next available payday. On a cumulative code, any over- or underpayment from earlier in the year is usually corrected automatically across your remaining pay periods.

How Your Tax Code Interacts with Self Assessment

This is where tradespeople with mixed income need to pay attention. Your PAYE tax code handles tax on your employment or director's salary throughout the year. Your Self Assessment return brings everything together — employment income, self-employed profits, dividends and any other income — and works out your true total tax bill.

Any difference between what your tax code collected and what you actually owe is squared up on the return. If your code took too much, you're due a refund. If it took too little — common when company benefits or a side trade weren't fully reflected in the code — the balance becomes payable. HMRC may then adjust next year's code to start collecting an underpayment, or you can pay it directly. Keeping your code accurate during the year keeps these year-end adjustments small and predictable.

What to Do If You've Overpaid or Underpaid

If you've overpaid

Overpayment usually comes from emergency codes, a 0T or BR code applied for too long, or a benefit that was removed but never updated. Within the current tax year, correcting the code often refunds the overpaid tax automatically through your pay. After the year ends, HMRC reconciles your record and issues a P800 calculation if you're owed money, which you can usually claim back online. If you file Self Assessment, the refund comes through your return.

If you've underpaid

Underpayments build up when too much allowance was given, a benefit wasn't taxed, or a second income wasn't coded properly. HMRC will either adjust a future tax code to collect the shortfall gradually, or ask you to pay it — and through Self Assessment it forms part of your balancing payment. Don't ignore an underpayment notice: act on it early so you can plan the cash and avoid a larger bill landing at once.

Quick Reference: Common UK Tax Code Letters (2025/26)

Figures and thresholds shown are for the 2025/26 tax year and can change at fiscal events such as the Budget. If in doubt about your own situation, check your Personal Tax Account or speak to your accountant.