You open your payslip and see C1257 W1. It looks like a password, but it is just four pieces of information. Here is exactly what each part means, whether you are paying the right tax, and what to do if it does not change.
The short answer: C1257 W1 means you are treated as a Welsh taxpayer with the standard £12,570 tax-free allowance, but your employer is calculating tax one pay period at a time instead of across the whole year. It is normally a temporary “emergency” basis, and you may be overpaying until it is corrected.
Breaking Down the Code
HMRC treats you as living in Wales for tax purposes, so your employer applies the Welsh rates of income tax. Scottish taxpayers get an “S” instead.
Multiply by 10 to get the tax-free amount you can earn in the year: £12,570, the standard personal allowance.
L is the usual letter for a standard personal allowance. HMRC often shows the code as C1257L, and some payslips drop the L.
Also seen as M1 for monthly pay. Each payday is treated as a fresh start, so allowance you did not use earlier in the year is not carried forward. This is the emergency basis.
What Does W1 Actually Do?
Normally your tax code works on a cumulative basis. Each payday your employer looks at everything you have earned since April and the allowance you have built up, so any over or underpayment evens itself out.
On a W1 or M1 basis, that memory is switched off. Your employer gives you one week’s (or one month’s) slice of the allowance and the basic-rate band against that pay only. Nothing is carried over from earlier months.
That is why it is used as a safety net. If HMRC does not yet have your pay and tax to date, a refund cannot be safely worked out, so the emergency basis avoids giving you too much allowance. The downside is that you can end up paying more tax than you need to for a while.
| Normal (cumulative) | W1 / M1 (emergency) | |
|---|---|---|
| Looks at | Your whole year to date | Only the current pay period |
| Unused allowance | Carried forward | Lost for that period |
| Over or underpaid tax | Corrects itself | Not corrected until the code changes |
| Bonuses and one-offs | Spread across the year’s allowance | Can be taxed more heavily |
| Intended to be | Your normal code | Temporary |
Why Did I Get a W1 Code?
- New job without a P45 and HMRC has not yet received your pay details
- Starting a second job or going back to work after a gap
- A late or missing starter checklist from your employer
- A first pay run before HMRC’s records have updated after a change of employer
- HMRC changed your tax code mid-year and told your employer to restart the calculation
Tax Code Decoder
Type any UK tax code from your payslip. Free tool by Beck Hill Ltd.
Try C1257L W1, 1257L M1, S1257L, 1100T, BR, 0T or K475.
Am I Overpaying on W1?
Estimate how much extra tax one W1 or M1 payslip can take.
This is for someone whose earlier pay in the year was not through this job, for example a new starter. If you were paid by this employer since April, your cumulative tax would already include that pay.
Illustrative only. Assumes the 2026/27 UK rates, a C1257L code, a single job, no benefits or student loan, and that the cumulative calculation would apply from your first payslip. Your actual tax depends on your own records.
Is C1257 W1 Costing Me Money?
It might, but usually only temporarily. Because W1 ignores the allowance you have not used, the longer into the tax year you are, the more you could overpay if you started a new job late. Starting in April, W1 and cumulative are nearly identical. Starting in October without any earlier pay through that job, the difference can be several hundred pounds across a few payslips (try the estimator above).
The good news is that this is normally put right automatically. Once your employer sends HMRC your first Full Payment Submission, HMRC issues a new code on the normal cumulative basis, and any tax you overpaid is corrected through your pay.
Do not ignore it. If C1257 W1 is still on your payslip after two or three pay cycles, something has not updated. Check your tax code in your HMRC personal tax account, make sure your employer has your correct details, and ask HMRC to confirm the code.
What Should I Do About It?
- Check you have been given the right code. The C is correct if you live in Wales, and 1257 is correct if you have no benefits, other income or unpaid tax to collect.
- Give your employer your P45 if you have one, or complete the starter checklist accurately, ticking the right statement about your other income.
- Look at your next payslip. The W1 should drop off within one or two pay cycles.
- Check your HMRC personal tax account to see the code HMRC thinks you should be on, and your income and tax to date.
- If it does not change, contact HMRC or ask us to deal with it on your behalf. You can claim back any tax you overpaid.
What Does the C Mean for My Tax?
Since April 2019 the Welsh Government has had the power to set the Welsh rates of income tax on earnings, pensions and self-employed profits. HMRC marks Welsh taxpayers with a C so employers know to apply them.
At present Wales has kept its rates the same as the rest of the UK: 20% basic, 40% higher and 45% additional. In practice a Welsh taxpayer on C1257L currently pays the same income tax as an English taxpayer on 1257L. Dividends and savings income are not devolved, and National Insurance is not affected by Welsh rates.
Who counts as a Welsh taxpayer is not decided by where you work or your employer’s address. It depends on where you have your main place of residence during the tax year. If you move into or out of Wales, tell HMRC so your code is updated.
| Code | Meaning |
|---|---|
| 1257L | Standard allowance, rest of UK, cumulative |
| C1257L | Standard allowance, Welsh taxpayer, cumulative |
| S1257L | Standard allowance, Scottish taxpayer, cumulative |
| C1257L W1 | Welsh taxpayer, standard allowance, week 1 emergency basis |
| C1257L M1 | Welsh taxpayer, standard allowance, month 1 emergency basis |
| CBR | Welsh taxpayer, all pay taxed at the basic rate |
| C0T | Welsh taxpayer, no allowance |
Frequently Asked Questions
C shows you are a Welsh taxpayer, 1257 means a £12,570 tax-free personal allowance, and W1 means your tax is calculated on a week 1 or month 1 basis, so each pay period stands alone and nothing carries forward.
The W1 part is the emergency basis. It is often used when HMRC does not yet have your previous pay and tax details, for example when you start a new job without a P45. It is normally temporary.
If you were overtaxed, HMRC or your employer normally corrects it once your code switches to the cumulative basis, which can show as a refund in your pay. If you have stopped working or it is not corrected, you can claim it back from HMRC.
No. At present the Welsh Government sets the Welsh rates at the same level as the rest of the UK, so the C prefix changes who receives the tax, not how much you pay.
Not directly. HMRC issues your code and tells your employer. You can update the information it uses through your personal tax account or by contacting HMRC. If you are not sure, we can do it for you.
This guide is general information based on 2026/27 rates and is not personal tax advice. Your code depends on your own circumstances. See GOV.UK: Tax codes for HMRC’s official guidance.
Not Sure Your Tax Code Is Right?
Beck Hill Ltd can check your code, deal with HMRC to get any overpaid tax back, and make sure your payroll is set up correctly. We help individuals and businesses in Neath, Port Talbot, Swansea and across Wales and the UK.
Check My Tax Code Call: 07588 603827
