What does the tax code
1231L mean?

Most people land on 1231L holding a P2 coding notice they have just opened. The code means your Personal Allowance for 2026/27 is £12,310 rather than the standard £12,570, so HMRC has taken £260 off. The notice in your hand names the reason. The trouble is that the wording HMRC uses is rarely the wording anyone would use, so the line that explains everything often reads like it explains nothing.

1231L Tax Code

A tax code giving a Personal Allowance of £12,310 for 2026/27, which is £260 below the standard figure. The L suffix means the ordinary allowance rules apply. The reduction is a deduction HMRC has made for something it believes reduces your entitlement, most often a small taxable benefit from your employer or the recovery of tax you underpaid in a previous year.

The single most misread thing about 1231L

A £260 deduction is not a £260 bill.

The number in your code is an amount of allowance, not an amount of tax. Cutting £260 off your allowance means £260 more of your income gets taxed. At the basic rate that costs you £52 across the year, which is £4.33 a month. At the higher rate it costs £104.

This matters because the two most common causes of a deduction behave completely differently, and confusing them leads people to argue with HMRC about the wrong number.

If the deduction is a benefit in kind, the figure is the value of the benefit. A taxable benefit worth £260, say a modest employer-paid subscription or a small insurance policy, produces a £260 deduction and costs you £52 in tax at the basic rate. Deduction and benefit are the same number.

If the deduction is underpaid tax being collected, the figure is not the debt. HMRC works backwards: it takes the tax you owe and grosses it up by your marginal rate to find the allowance reduction that will collect it. A £260 reduction at the basic rate recovers £52 of debt across the year, not £260. To collect an actual £260 debt from a basic rate taxpayer, HMRC would need to cut your allowance by £1,300 and your code would read 1127L, not 1231L.

So if you are on 1231L and you think you owe HMRC a couple of hundred pounds, the arithmetic says this code is not collecting it.

What your P2 coding notice is telling you

Your coding notice sets out the sum. It starts with the standard allowance, lists each addition and deduction, and lands on the total that becomes your code.

If your notice shows several smaller deductions adding up to £260, the same logic applies to each one. Read every line, not just the total.

Worked example: 1231L on a £24,000 salary

An office administrator earning £24,000 whose employer provides a small private medical policy.

1. Gross salary: £24,000
2. Deduct the 1231L allowance: £24,000 minus £12,310 = £11,690 of taxable income
3. Everything falls inside the basic rate band, so it is taxed at 20%
4. Income tax for the year: £2,338
5. Monthly tax-free pay: £12,310 divided by 12 = £1,025.83

On the standard 1257L code the same salary would produce £11,430 of taxable income and £2,286 of tax. The difference is £52 for the year, or £4.33 a month. These are income tax figures only, exclude National Insurance, and are an estimate to confirm with HMRC.

The £52 does not change if you earn more, provided you stay inside the basic rate band. At £38,000 the tax is £5,138 on 1231L against £5,086 on 1257L, the same £52 gap. It only grows once income passes £50,270, at which point the £260 is being taxed at 40% and the cost doubles to £104.

What happens to 1231L next April

Codes are reissued for every tax year, and this is where a small deduction quietly becomes a permanent one.

When HMRC builds your code for the following year, it starts from the record it already holds. A benefit in kind that your employer reported last year is assumed to be continuing unless something says otherwise. An estimate of untaxed interest is rolled forward. Neither is re-examined from scratch. So a £260 deduction that was correct in the year it appeared can sit in your code for years after the thing that caused it has gone.

There is one exception worth knowing about. A deduction that exists purely to recover an underpayment is meant to be temporary: once the debt is collected, it should drop out and your code should return to the standard figure. If you were told a deduction was collecting an old underpayment two or three years ago and it is still there, that is a specific and answerable question to put to HMRC.

The practical habit is to read the P2 coding notice each spring rather than filing it. It is a one-page statement of every assumption HMRC is making about you, and it is the only moment in the year when those assumptions are laid out plainly.

When 1231L is wrong

The deduction is only as good as the information HMRC holds, and that information comes from your employer and from estimates. Three situations produce a wrong 1231L.

The benefit ended and nobody told HMRC. Employer benefits are reported annually. If your medical cover, subscription or other perk stopped part way through a year, the deduction can survive into the next year unchanged. You are then paying tax on something you no longer receive.

The estimate is too high. Deductions for untaxed interest are estimates based on what HMRC saw in an earlier year. Interest rates move and balances get spent. If HMRC is assuming interest you are not actually earning, the deduction is fiction and you can ask for it to be revised.

The underpayment was already settled. If you paid an earlier bill directly and HMRC also coded it out, you are paying twice. This is worth checking carefully, because the two systems do not always talk to each other quickly.

If any of those apply, the position for closed years may also need putting right, which is a separate exercise from fixing the code. Our guide to reclaiming overpaid tax sets out the four-year claim window and how to use it.

How to get 1231L changed

Sign in to your Personal Tax Account at gov.uk/personal-tax-account and open "Check your Income Tax". The service shows every addition and deduction behind your code and lets you tell HMRC when a benefit has ended or an estimate is wrong. Our step-by-step guide to checking your tax code walks through where to find each figure.

If you would rather speak to someone, the Income Tax helpline is 0300 200 3300, open Monday to Friday. Have your National Insurance number, your current code and the coding notice in front of you.

When HMRC issues a replacement code mid-year, the correction is applied cumulatively, so any tax you overpaid earlier in the year comes back through your next payslip in one go. For a deduction this small the refund will be a few pounds, but the principle is the same for the much larger deductions covered on our K tax code and T tax code pages.

Before you call, run your figures through the free tax code checker so you arrive with a number rather than a suspicion. It produces an estimate, not advice, and HMRC has the final word.

People also ask

What does tax code 1231L mean?

1231L means your tax-free Personal Allowance for 2026/27 is £12,310, which is £260 below the standard £12,570. The L suffix means the ordinary allowance rules apply. The £260 is a deduction HMRC has made, most commonly for a small taxable benefit from your employer, an estimate of untaxed interest, or tax underpaid in an earlier year being collected through your pay.

How much extra tax do I pay on 1231L?

About £52 a year if you are a basic rate taxpayer, which is £4.33 a month, and about £104 a year if you pay higher rate. The £260 is a reduction in allowance rather than a tax charge, so the cost to you is the tax on that £260 at whatever rate applies to the top slice of your income.

Does 1231L mean I owe HMRC £260?

No, and this is the most common misreading of the code. If the deduction is recovering underpaid tax, HMRC grosses the debt up by your marginal rate first, so a £260 allowance reduction collects roughly £52 from a basic rate taxpayer across the year. An actual £260 debt would require a £1,300 reduction and a code of about 1127L.

Why did my tax code change from 1257L to 1231L?

Something was added to HMRC's record of your circumstances that reduces your allowance by £260. The usual triggers are an employer reporting a new taxable benefit, HMRC adding an estimate of untaxed interest or other income, or a reconciliation finding you underpaid tax in an earlier year. Your P2 coding notice names the specific reason on the deduction line.

Is 1231L a normal tax code?

Yes. It is an ordinary cumulative L-suffix code and there is nothing unusual or penal about it. It simply reflects a small adjustment to your entitlement. It is worth checking rather than ignoring, because deductions tend to persist in your code long after the thing that caused them has ended.

Related tax codes: 1257L tax code | 1226L tax code | T tax code | K tax code | Wrong tax code?

HMRC: What your tax code means