Tax Code · 2026/27
W1 / M1 / X Tax Code Suffix: Non-Cumulative PAYE
W1, M1 and X suffixes mean your PAYE is calculated on a non-cumulative basis - each pay period treated in isolation, ignoring year-to-date earnings. You get 1/52 or 1/12 of your Personal Allowance each period.
What the W1 / M1 / X tax code means
A regular cumulative tax code (like 1257L on its own) calculates tax based on total earnings since 6 April. PAYE looks at how much PA and basic-rate band you have used year-to-date and corrects in each payslip.
Adding W1, M1 or X strips that cumulative calculation: each payslip is treated as a standalone tax event. You get 1/12 of the PA in a monthly payslip (£1,047.50) or 1/52 in a weekly one (£241.73), and your basic rate band is similarly sliced.
The non-cumulative basis prevents large refunds or large bills if your year-to-date figure is uncertain. HMRC uses it as a safety mechanism in the first few payslips of a new job, or after a major change (like a tax-code reset).
When you'll see W1 / M1 / X
- You started a new job mid-tax-year and provided a P45, but HMRC has not yet caught up - the W1/M1 prevents PAYE refunding tax against unknown prior-employment figures.
- You returned to PAYE after a period out of work (maternity, sabbatical, self-employed) and HMRC is rebuilding your year-to-date position.
- A material tax code change mid-year - HMRC may apply the new code on a non-cumulative basis until April to avoid a one-off massive refund.
- Pension drawdown or one-off taxable lump sums - providers often apply emergency M1 on first payment.
What to do if you have a W1 / M1 / X code
- For most new starters: provide your P45 from the previous employer immediately. HMRC usually converts W1/M1 to cumulative within 1-2 pay periods once year-to-date figures match up.
- Check your Personal Tax Account (gov.uk/personal-tax-account) - look for the tax code notice explaining why non-cumulative basis is applied.
- If you think the year-to-date figures are wrong or the W1/M1 is unjustified, call HMRC on 0300 200 3300 with your NI number.
- Any over-tax under W1/M1 is normally refunded automatically through subsequent payslips once HMRC moves you to cumulative basis, or via a P800 reconciliation after year-end.
Worked example
On 1257L M1 at £4,000 monthly gross: only 1/12 of PA applied = £1,047.50 PA, taxable £2,952.50, tax at 20% = £590.50/month. On 1257L cumulative at the same £4,000 monthly: if it is month 6 and YTD earnings £24,000, total PA used £6,285, taxable £17,715, tax at 20% = £3,543 YTD - same monthly tax of £590.50. The difference only matters when YTD pattern is uneven (large bonus mid-year, returning from leave, etc.).
Want to see the numbers for your own salary? Use the salary calculator and pick 2026/27 to see how W1 / M1 / X interacts with your full take-home.
Frequently asked questions about W1 / M1 / X
- What is the difference between W1, M1 and X?
- W1 is applied to weekly payrolls, M1 to monthly. X is a generic non-cumulative suffix used for any other frequency (4-weekly, fortnightly, daily) or when payroll software does not differentiate. Functionally identical - all three strip the cumulative calculation.
- Why is "0T non cumulative tax code" so common?
- New starters without a P45 are frequently coded 0T W1/M1 or 0T X by employers. This combination strips both the Personal Allowance AND the cumulative calculation - the most punitive standard combination - until HMRC issues a corrective code. Providing a Starter Checklist on day one usually avoids this.
- Will HMRC refund tax automatically?
- Yes - once HMRC moves you to a cumulative code (no W1/M1/X suffix), the first cumulative payslip rebalances year-to-date totals and any over-paid tax flows back through that payslip. If the year ends first, the automatic year-end reconciliation produces a P800 with refund instructions, usually issued June-November.
- Does W1/M1 affect my pension contributions?
- No - W1/M1 affects only Income Tax PAYE calculation. Pension contributions (workplace auto-enrolment, salary sacrifice, relief at source) and National Insurance use their own calculation rules that are unaffected by the cumulative/non-cumulative basis of Income Tax.
Related tax codes
- 1257L
1257L is the default UK tax code for 2026/27. It gives you the full £12,570 Personal Allowance before Income Tax is deducted - the number 1257 is your allowance divided by 10, and the L means a standard untouched allowance.
- 0T
0T (zero-T) gives you no Personal Allowance. Tax is calculated on every pound of your pay using the normal bands (20%, 40%, 45%) as if your whole income is taxable.
- 1257L W1/M1/X
An 'emergency' tax code is a non-cumulative version of your main code. You'll see W1 (weekly), M1 (monthly), or X (either) appended - each pay period is taxed in isolation, which usually means you pay more tax than you owe.
- BR
BR stands for 'Basic Rate'. It taxes 100% of pay from that source at 20%, with no Personal Allowance. HMRC uses it most often on second jobs and pensions, where your £12,570 PA is already used up by the main income.
Sources & further reading
All figures and definitions on this page reflect the 2026/27 UK tax year and are cross-checked against HMRC guidance.
- HMRC — What your tax code means (official meanings for L, BR, D0, D1, K, 0T, NT, M, N, S, C, T)
- HMRC — Income Tax rates and Personal Allowance (2026/27 bands and thresholds)
- HMRC — Emergency tax codes (W1, M1 and X suffixes)
- HMRC — Rates and thresholds for employers 2026 to 2027
- HMRC — Your Personal Tax Account (check your current code and how it was calculated)
- Our methodology & calculation sources →