What is a Tax Code and How Does Yours Work?

A tax code is a short string of numbers and letters that tells your employer or pension provider how much tax-free pay you’re entitled to before income tax comes off. HMRC sets it, your employer applies it. The number carries your allowances for the tax year, and the letter explains your circumstances.

Your code sits in small type on your payslip, easy to scroll past. It’s also the one line there that HMRC controls rather than your employer, and when it’s wrong nothing announces it. The money just doesn’t arrive.

PAYE is designed to collect the right tax steadily as you’re paid, rather than settling up in one go after the year ends. That only works when the code is right.

Spotting a wrong one is your job, not your employer’s. HMRC’s guidance is clear about it, which is why understanding your tax code is what stops an error running for months before anyone catches it.

A code makes itself felt at particular moments: starting a job, a first pension payment, a company car arriving, or a payslip that’s lighter than the last one for no obvious reason. Each of those is a point where the number can move, and where a wrong one can start running unnoticed.

What a tax code is made up of

Nearly every code splits into two parts, and each part does a different job.

Take 1257L, the standard code for the 2026/27 tax year. The 1257 is your tax-free pay for the year with the final digit removed, so £12,570 becomes 1257. If you’ve wondered what do the numbers in my tax code mean, that’s the whole trick.

The L is a shorthand for your circumstances, in this case entitlement to the standard personal allowance and nothing unusual on top. There’s a fuller breakdown in the 1257L tax code guide.

Pull a code apart and you get up to four elements:

• The number, which stands for your tax-free pay across the year, minus its last digit.
• The letter, which tells payroll which rule applies to you.
• Anything in front, like an S or a C, which sets whose income tax rates apply.
• Anything after, W1 or M1 for instance, which changes how the calculation runs each payday.

So how does a tax code work once payroll has it? Your employer spreads that tax-free amount evenly across the year rather than handing it over in one go.

On monthly pay, a 1257L code gives roughly a twelfth of £12,570 free of tax each time. The code itself doesn’t set a tax rate, with the exception of a few flat-rate codes covered further down.

How is my tax code worked out?

HMRC starts with what you’re allowed to earn tax free, then subtracts anything it wants to tax through the code rather than separately.

The calculation runs in three steps:

• Add up your allowances, starting with the personal allowance and adding anything else you’re entitled to, such as job expenses.
• Add up your deductions, meaning income HMRC expects you to receive with no tax taken off, plus any tax owed from an earlier year.
• Subtract the deductions from the allowances to get your tax-free pay for the year, then drop the final digit to get the number in your code.

So how are tax codes calculated in practice? Allowances minus deductions, divided by ten, rounded down. Someone entitled to £12,570 with a company car worth £3,000 in taxable benefit has £9,570 of tax-free pay left, which becomes 957L.

Deductions are the part that catches people out. A company car, private medical cover, untaxed savings interest, the state pension and tax owed from a previous year can all pull the number down, even though none of them show up on your payslip as income from that job.

The link between your tax code and personal allowance is direct but not identical: the allowance is where the sum starts, and the code is where it ends up.

Tax code letters explained, from L to NT

The letter isn’t decoration. It tells payroll which rule to apply, and changing one letter changes what lands in your account. GOV.UK publishes the full list of tax code letters.

Here’s what do the letters in my tax code mean, in plain English:

• L means you get the standard personal allowance with no adjustment.
• M means your spouse or civil partner has transferred 10% of their allowance to you, and N means you’ve transferred 10% of yours to them.
• T means the code contains a calculation HMRC wants to review, often where income is high enough for the allowance to taper.
• BR taxes everything from that source at the basic rate, with no allowance applied at all.
• D0 and D1 do the same job at the higher and additional rates.
• 0T applies no allowance either, but unlike BR it still works through the rate bands as your pay rises.
• NT means no tax is deducted from that income.
• K means your deductions come to more than your allowances, so you get extra taxable pay added rather than tax-free pay taken away.

That last one deserves a pause, because a K code works backwards compared with the others. Instead of reducing what you can earn tax free, it adds an amount to the pay your employer taxes, which is why a K code can look like tax coming off money you never saw.

The difference between a standard tax code and BR is the same idea in reverse: a standard code hands you an allowance to use here, while BR assumes another job or pension is already using it.

Why some codes start with S or C

Income tax rates aren’t identical across the UK, so the code has to say where you live.

An S at the front means Scottish rates and bands apply, and a C means Welsh rates apply. The personal allowance is the same wherever you live, so S1257L and 1257L both give £12,570 of tax-free pay.

What changes is what’s charged above that, and Scotland runs a different set of bands from the rest of the UK. The guide to tax codes in Scotland sets out how the rates differ.

The prefix follows your main home, not your employer’s address. Move across the border and your code can change even though nothing at all has changed about your job.

Emergency codes tax each payday on its own

Most codes are cumulative. Payroll looks at everything you’ve earned and paid so far this year and evens the tax out as it goes. An emergency code doesn’t do that.

Codes ending W1, M1 or X run on a non-cumulative basis, and some payroll systems show NONCUM instead. Tax is worked out on that single week or month in isolation, as though you were paid the same amount in every period of the year.

It applies where a new employer hasn’t yet been given your earlier pay and tax figures, and it can also turn up when company benefits or the State Pension start. The guide to emergency tax codes covers the variations.

Because the calculation ignores the rest of the year, an emergency code can leave you paying too much tax or too little. HMRC usually replaces it once it has gathered your details from both the old and new employer, which it says can take as long as 35 days from your first day.

If you have not paid enough, the emergency code stays in place until the right tax for the year has been collected.

If you have paid too much, you can claim the difference back.

Why has my tax code changed?

A new code landing part way through the year usually means HMRC has learned something new about your income.

When do I get a new tax code? Before each tax year starts, and again whenever something shifts: a new job, a benefit starting or stopping, a marriage allowance claim going through, savings interest reported by your bank, or tax from an earlier year being collected through your pay.

Can my tax code change mid year? Yes, and it’s supposed to. A code that never moved would be a code that had stopped tracking your circumstances.

A P2 notice of coding sets out what makes up your code and gives an explanation of each item in it. HMRC sends one when it sets or changes your code, online or by post. Your employer receives the code separately and electronically, which is why a change can appear on your payslip before the paperwork reaches you.

Where to check your tax code and put it right

Your code appears on every payslip, on your P45 when you leave a job, on your P60 after the tax year closes, and on any coding notice HMRC sends you.

The most useful check is HMRC’s own. Your personal tax account and the HMRC app both show your current code and, more to the point, the figures sitting behind it, so you can see which benefit or allowance is driving the number. GOV.UK also has a tool that explains what a tax code means without asking you to sign in.

Only HMRC issues a code. Your employer’s job is to apply the one it’s given, so a wrong code has to be put right at HMRC’s end, usually by checking and updating the employment, income and benefit details it holds about you.

There’s more in the guide to what to do if your tax code is wrong. One thing does belong with your employer, though: if HMRC has issued a new code and your payslip still shows the old one, check that payroll has received it.

Where a correction lands during the tax year, the adjustment usually comes through your pay. After the tax year ends, HMRC checks the tax paid across all your income, and where the amount was wrong it sends a P800 calculation showing either a refund due or tax owed.

Checking your tax code: what to do next

Two parts, one job. The numbers carry your tax-free pay for the year, the letter carries your circumstances, and HMRC builds the number by taking your allowances, subtracting whatever it wants to tax through the code, and dropping the last digit.

That’s your tax code explained in a sentence, and it answers what does my tax code mean for the money that actually reaches your account.

Codes change when circumstances change, and nobody else checks them on your behalf. The habit worth having is looking at the code on your payslip whenever it moves, then comparing the figures behind it in your personal tax account against what’s actually true of your income this year.

If it’s wrong, HMRC is the only place it can be put right. The personal allowance guide sets out the figure most codes are built from.

Key takeaways

The short version, if you’re checking your own code against it:

• A tax code tells your employer how much of your pay is tax free, and it doesn’t set a tax rate on its own.
• The number is your tax-free pay for the year with the final digit removed, so 1257L reflects a £12,570 allowance.
• The letter describes your circumstances, from the standard allowance under L to flat-rate deduction under BR, D0 and D1.
• An S or C prefix decides whose income tax rates apply, and a W1, M1 or X suffix makes the code non-cumulative.
• Company benefits, untaxed income and tax owed from earlier years all pull the number in your code down.
• Only HMRC can issue a new code, and HMRC guidance puts the job of spotting an error on the taxpayer.

Common tax code questions

The questions below sit outside the basic mechanics, and GOV.UK’s tax code guidance is the reference point for each of them.

Do I get a tax code if I’m self-employed?

Not for your self-employed profits. Tax codes belong to PAYE, which covers employment and pension income, and they work by telling a payroll how much to deduct before paying you. Nobody deducts tax before paying a self-employed person, so there’s nothing for a code to instruct. That income goes through Self Assessment instead, where the tax is worked out and paid after the tax year ends.

Plenty of people have both. If you hold a job alongside self-employment, that job carries a tax code like any other, and the code applies only to what the employer pays you. The self-employed side stays outside it entirely.

There is one crossover worth knowing about. Where a Self Assessment bill comes to less than £3,000 and you already pay tax through PAYE, HMRC can collect that bill through your tax code across the following year rather than asking for it in a single payment. Filing the return by the online deadline in late December is what makes it possible, and the number in your code drops to make room for the amount owed.

Is my tax code the same as my personal allowance?

No, though they’re closely related. The personal allowance is a fixed amount set by government and shared by most taxpayers. Your tax code is a personal instruction to one payroll, built from that allowance and then adjusted for everything specific to you.

Two people entitled to exactly the same personal allowance can end up with very different codes. A company car, untaxed interest, a marriage allowance transfer or an underpayment being collected will each move the number, in one direction or the other.

So the code tells you what you can earn tax free from that particular source this year, which may be more or less than the headline allowance figure.

How long does HMRC take to change a tax code?

HMRC publishes a timescale for this. Where your code needs to change, HMRC says it will update the code and tell both you and your employer the new one within 15 working days.

After that it comes down to your pay cycle. If you’re paid monthly, the new code should show on your next payslip or the one after it. If you’re paid weekly, expect it by the third payslip. If it hasn’t appeared by then, check with your employer that payroll has received it.

Starting a new job is the exception. HMRC asks you to wait 35 days from your start date before getting in touch, because it needs that time to gather your income details from your old and new employers.

How often should I check my tax code?

There’s no required frequency, but two moments make obvious sense. The first is when a new code arrives, usually shortly before the start of a tax year. The second is any time your circumstances move.

Changes worth a look include starting or leaving a job, picking up a second job or pension, a company benefit starting or stopping, claiming or cancelling marriage allowance, drawing a pension for the first time, or income rising past the point where the allowance starts to taper.

Looking at the code on your payslip each April, and again after anything on that list, covers the situations where codes drift out of date.

Does my tax code change if I get a pay rise?

Usually not. The code sets how much of your pay arrives tax free, not the rate charged on the rest. Earn more and a larger slice of your income falls into the higher bands, but the tax-free amount hasn’t moved, so the code has no reason to move either.

The exception sits at the top of the scale. Once income passes £100,000 the personal allowance starts to taper away, falling by £1 for every £2 above that line and disappearing entirely at £125,140. HMRC adjusts the code to match, so a rise that crosses into that band does change the number.

What GOV.UK actually lists as triggers for a code change are different things: starting a new job, income from a second job or pension, savings interest above your allowance, a company benefit starting or stopping, claiming marriage allowance, or tax owed from an earlier year being collected. A pay rise from the same employer isn’t among them. So if your code shifts in the same month as a rise, the cause is worth looking for somewhere else.