The 1257L W1 tax code on your payslip means HMRC has given you the standard £12,570 personal allowance but told your employer to calculate your tax week by week instead of across the whole tax year. It’s an emergency code, usually applied when you start a new job without handing over a P45, and it often leaves you paying more tax than you should until HMRC gets the information it needs to switch you to a normal cumulative code.
What the Numbers and Letters Actually Mean
The 1257 stands for your tax-free personal allowance of £12,570, the amount you can earn each tax year before income tax kicks in. That figure has been frozen since April 2022 and is set to stay there until at least April 2031.1UK Parliament. Direct Taxes: Rates and Allowances for 2026/27
The L means you get the full basic allowance with no adjustments. If you were transferring part of your allowance to a spouse through Marriage Allowance, or earning over £100,000 (where the allowance tapers away), you would see a different letter.
The W1 is the part causing you problems. It stands for “week 1” and tells payroll to treat every pay period as if it were the first week of the tax year. A normal cumulative code tracks everything you’ve earned and paid in tax since 6 April, then adjusts each payday to keep you on track for the year. W1 throws that history out. Every week starts from zero.
If you’re paid monthly, the same logic appears as M1 on your payslip. Occasionally an X suffix shows up instead; X works similarly but may not apply your full allowance at all.2GOV.UK. Tax Codes: Emergency Tax Codes W1, M1, and X are all emergency codes, and all are temporary.
Why You Ended Up on an Emergency Code
The most common reason is starting a new job without giving your employer a P45 from your last one. The P45 shows your year-to-date pay and tax, which the new payroll system needs to run your code cumulatively. Without it, HMRC plays safe and uses a non-cumulative code so you don’t accidentally receive allowance you’ve already used.2GOV.UK. Tax Codes: Emergency Tax Codes
If you didn’t have a P45, your employer should have asked you to complete a starter checklist, which collects your National Insurance number, information about other jobs or benefits since 6 April, and student loan details.3GOV.UK. Starter Checklist if You’re Starting a New Job The checklist helps HMRC get you onto the right code, but there’s usually a lag.
Other situations that can trigger W1 or M1:
- Returning to work after a period of unemployment, when HMRC lacks recent data.
- Starting a company car, private health cover, or other taxable benefit part way through the year.
- Moving from self-employment into a PAYE job, where there’s no payroll history for the new employer to pick up.
- Taking on a second job, which can confuse where your personal allowance sits until HMRC allocates it.
How It Affects Your Take-Home Pay
Under W1, payroll divides your £12,570 allowance into 52 weekly slices of roughly £241.73. M1 splits it into 12 monthly slices of £1,047.50. Only that single slice is applied against your earnings in the pay period, and anything above it is taxed at the relevant rate.
The problem shows up when your earnings across the tax year haven’t been steady. Say you started a new job in September after not working since April. A cumulative code would recognise five months of unused personal allowance and apply it to your September pay, leaving you with little or no tax that month. W1 ignores those months entirely. You get one week’s worth of allowance, and the rest of your pay is taxed. You end up handing over more than you owe.
It can go the other way too. If you earned heavily earlier in the year and moved to a lower-paying role, W1 keeps handing you a fresh slice of allowance each week regardless of what you’ve already used. That’s why HMRC treats the code as a safety net: it prevents big errors in either direction while it waits for accurate data.
How to Get Switched to a Cumulative Code
The fastest route is your Personal Tax Account on GOV.UK, or the HMRC app.4GOV.UK. Personal Tax Account: Sign In or Set Up Signing in for the first time requires identity verification with photo ID. Once you’re in, you can check your current code, see recent changes, and report information that affects it.5GOV.UK. Check Your Income Tax for the Current Year
Have a few things ready. Your most recent payslip gives your gross year-to-date pay and total tax deducted. A P45 from your previous employer, if you have one, contains the exact figures HMRC needs. You’ll also want an estimate of your full expected income for the year, including any second job, taxable benefits, or investment income. Earnings above £50,271 fall into the 40% higher rate, so accurate figures matter if you’re anywhere near that threshold.6GOV.UK. Income Tax Rates and Personal Allowances
Once HMRC processes the update, it sends a new coding notice directly to your employer’s payroll.7GOV.UK. Understanding Your Employees’ Tax Codes The change typically takes one to two pay cycles to appear. When your employer switches you to a cumulative code, any tax overpaid while on W1 is normally refunded automatically through your next payslip.
If you prefer to phone, the income tax helpline is 0300 200 3300, Monday to Friday 8am to 6pm. Have your National Insurance number to hand.8GOV.UK. Income Tax: Enquiries One limitation: if you pay tax only through Self Assessment, you can’t use the online service to change your code and will need to call instead.5GOV.UK. Check Your Income Tax for the Current Year
What Happens if the Code Isn’t Fixed Before Year-End
Emergency codes don’t follow you forever. At the start of the new tax year in April, HMRC replaces them with a standard cumulative code.9GOV.UK. Tax Codes: If You’ve Paid Too Much or Too Little Tax After the year ends, HMRC pulls together your pay and tax data from employers, pension providers, and the benefits office to check whether you’ve paid the right amount overall.
If the numbers don’t reconcile, you’ll get a P800 tax calculation letter, usually between June and November. It confirms whether you’ve overpaid or underpaid and by how much.10GOV.UK. Tax Overpayments and Underpayments: If Your Tax Calculation Letter (P800) Says You’re Due a Refund The reconciliation isn’t quick. If you’ve been on W1 all year and overpaid by hundreds of pounds, you may wait months for HMRC to work through it. That’s the strongest argument for updating your code proactively rather than sitting on it.
Claiming Back Overpaid Tax
Once your P800 confirms a refund is due, you can claim online through your Personal Tax Account or the HMRC app. You’ll need the reference number from the P800 and your National Insurance number. Bank transfers arrive within five working days. If you don’t claim within 45 days, HMRC sends a cheque.10GOV.UK. Tax Overpayments and Underpayments: If Your Tax Calculation Letter (P800) Says You’re Due a Refund
There is a hard deadline. You have four years from the end of the tax year in which the overpayment happened to make a claim. For the 2025/26 tax year, which ends on 5 April 2026, that means claiming by 5 April 2030. Miss the window and the year closes permanently. If you suspect a coding error has run across more than one tax year, check each year individually so nothing lapses.
Scottish and Welsh Prefixes
If you live in Scotland, your code carries an S prefix, so 1257L W1 becomes S1257L W1. The £12,570 allowance is the same, but the S tells payroll to apply Scottish income tax rates and bands, which differ from those used in England and Northern Ireland.11mygov.scot. Tax Codes Welsh residents see a C prefix (C1257L W1). Welsh rates have so far matched those in England and Northern Ireland, but the prefix is applied so that any future divergence can be processed automatically.
Working Two Jobs at Once
Your personal allowance can only be used once. When you hold two jobs at the same time, HMRC normally allocates the full 1257L allowance to one employer (usually the higher-paying one) and gives the second a BR code, which taxes every pound at the 20% basic rate with no tax-free portion.
If both jobs pay relatively little and your combined income stays below £12,570, you can ask HMRC to split your personal allowance between them. It’s worth reviewing the split if your hours change at either job. Contact HMRC through your Personal Tax Account or the helpline to set it up.
Multiple jobs are also where W1 problems most often appear. If you leave one job and start another before the P45 catches up, both employers can end up running emergency codes at the same time. You might briefly get your personal allowance twice, or not at all. Getting your P45 to the new employer promptly is the single most effective thing you can do to avoid the mess.