The 1255L tax code means HMRC has set your tax-free Personal Allowance at £12,550 for the year, which is £20 below the standard £12,570 that most employees receive under code 1257L. The adjustment is small and usually reflects either a minor underpayment of tax being clawed back from an earlier year or a low-value taxable benefit from your employer. Over a full year, the extra tax works out to roughly £4 at the basic rate.
What the Number and Letter Actually Mean
Every PAYE tax code is made of a number and a letter. The number is your tax-free allowance with the last digit removed, so 1255 stands for £12,550. Your employer’s payroll software takes that figure, spreads it evenly across your pay periods, and only taxes what you earn above it.1GOV.UK. Tax Codes: What Your Tax Code Means
The L on the end is the most common suffix. It means you’re entitled to the standard Personal Allowance with nothing unusual attached to your record. If you had a marriage transfer, Scottish residency, or a code with no allowance at all, the letter would be different. With L, you’re a straightforward case whose allowance has simply been nudged by a small amount.1GOV.UK. Tax Codes: What Your Tax Code Means
Why Yours Is 1255L Instead of 1257L
The standard code for the 2025/26 and 2026/27 tax years is 1257L, matching the frozen £12,570 Personal Allowance.2GOV.UK. Understanding Your Employees’ Tax Codes When HMRC gives you 1255L instead, they’ve shaved £20 off that allowance. There are three usual explanations.
The most common is unpaid tax from a previous year. Rather than send you a bill, HMRC prefers to recover small amounts by reducing your allowance in the current year, so the debt comes out of your pay gradually. A £20 reduction points to an underpayment of around £4.
The second is a small taxable benefit from your employer. Perks such as private medical insurance, professional subscriptions paid on your behalf, or other benefits in kind have a taxable value, and HMRC subtracts that value from your Personal Allowance.1GOV.UK. Tax Codes: What Your Tax Code Means Employers report these benefits on a P11D form after the tax year ends, and HMRC updates your code from there.3GOV.UK. Expenses and Benefits for Employers: Reporting and Paying
The third possibility is a small amount of untaxed income on HMRC’s record, such as savings interest that hasn’t had tax deducted at source. Whatever the trigger, you should receive a coding notice from HMRC explaining the change. That notice is where to look first if you want to know exactly why your code moved.
What 1255L Costs You in Real Money
With 1255L, you can earn £12,550 over the tax year before income tax applies. Paid monthly, that gives you about £1,045.83 in tax-free pay each month. Everything above that runs through the normal tax bands.4GOV.UK. Income Tax: How You Pay Income Tax
Take someone earning £30,000 a year. On 1255L, they’re taxed on £17,450 of income. On the standard 1257L, they’d be taxed on £17,430. The difference is £20 of extra taxable income, which at the 20% basic rate is £4 more tax over the whole year. It’s a rounding error in most household budgets, but it is a real reduction, and it will keep applying until HMRC changes your code again.
Larger allowance reductions work the same way but scale up. A code of 1100L, for example, would put an extra £1,570 of income into the taxable column compared with the standard code, so the underlying mechanic is worth understanding even when the current effect on your payslip is tiny.
How to Check Your Code Is Right
The quickest way to verify your code is the “Check your Income Tax” service on GOV.UK or the HMRC app. Sign in with your Government Gateway credentials. You may need photo ID to confirm your identity. Once inside, you can see your current code, view recent changes, update the income details HMRC holds for you, and tell them about anything that should affect your tax.5GOV.UK. Check Your Income Tax for the Current Year
Look for the coding notice that explains the £20 reduction. If it references a benefit you no longer receive, an underpayment you’ve already cleared, or income that isn’t yours, use the same service to correct the record. HMRC will send your employer a revised code, sometimes called a P6, and payroll will apply it.6GOV.UK. Understanding Your Employees’ Tax Codes – Changes The new code usually shows up within one or two pay cycles. If the correction means you’ve been overpaying so far this year, your payroll software should recalculate automatically and refund the excess through your next payslip.
One boundary worth noting: if you file a Self Assessment return, the online “Check your Income Tax” service won’t show your current year code. You’ll need to check through your Self Assessment account or contact HMRC directly.5GOV.UK. Check Your Income Tax for the Current Year
If the Code Was Wrong and the Year Has Already Ended
When an incorrect code causes an overpayment that isn’t fixed before April, HMRC generally issues a P800 tax calculation after the tax year closes. The letter tells you whether you overpaid or underpaid.
If you’re owed a refund, you can claim it online through your Personal Tax Account or the HMRC app, and the money arrives within five working days. A cheque takes up to six weeks. If the P800 says HMRC will send a cheque automatically, expect it within 14 days of the letter’s date. Refunds spanning multiple years are combined into a single payment.7GOV.UK. Tax Overpayments and Underpayments: If Your Tax Calculation Letter (P800) Says You’re Due a Refund
If the P800 shows an underpayment, HMRC usually recovers it the same way your 1255L code was probably created in the first place: by adjusting next year’s code downward so the extra tax comes out of your pay gradually. This is the standard approach for underpayments of £3,000 or less. Larger amounts may need to be paid directly.
So a 1255L code is not a mistake to panic about. It is HMRC’s routine method for handling small adjustments, and the cost to you is measured in single pounds rather than hundreds. The action worth taking is a two-minute check of your coding notice to confirm the reason matches your circumstances.