When does tax month 1 start?

Tax month 1 starts on 6 April and ends on 5 May. For the 2025/26 tax year, M1 is 6 April 2025 to 5 May 2025.

Why don't tax months match calendar months?

The UK tax year starts on 6 April (a quirk of the 1752 calendar change). Tax months follow this, running 6th to 5th, to provide 12 equal periods ending on 5 April.

How does a tax month relate to PAYE?

Cumulative PAYE codes apply year-to-date allowance based on the current tax month. M3 means 3/12 of the £12,570 allowance has been applied (£3,142.50).

What if I'm paid weekly?

Weekly payroll uses tax weeks (W1-W52/W53) rather than tax months. Each tax week is 7 days starting 6 April, regardless of calendar boundaries.

How many tax months in a year?

Always 12. Some years have 53 tax weeks but always 12 tax months.

What's the relationship between tax months and bonus payments?

A bonus paid on 6 April is in M1 of the new tax year, even if it relates to performance in the prior year. Plan large bonuses around 5/6 April carefully — the tax year of the bonus determines the rate band.

Do tax months affect annual leave or pension?

Pension annual allowance is per tax year (not month). Holiday pay accrues by calendar/contract — tax months are payroll concepts only.

Can I see tax months on my payslip?

Yes — most monthly payslips show 'Tax Month' (e.g. 'TM 5'). It tells you which 30-day period the pay is for, useful for matching to RTI submissions.

UK Tax Month Calculator 2025/26 | M1

All 12 tax months for 2025/26

UK tax months run 6th to 5th of consecutive calendar months. The 2025/26 schedule:

M1 — 6 April 2025 to 5 May 2025
M2 — 6 May 2025 to 5 June 2025
M3 — 6 June 2025 to 5 July 2025
M4 — 6 July 2025 to 5 August 2025
M5 — 6 August 2025 to 5 September 2025
M6 — 6 September 2025 to 5 October 2025
M7 — 6 October 2025 to 5 November 2025
M8 — 6 November 2025 to 5 December 2025
M9 — 6 December 2025 to 5 January 2026
M10 — 6 January 2026 to 5 February 2026
M11 — 6 February 2026 to 5 March 2026
M12 — 6 March 2026 to 5 April 2026

Tax months are not the same as calendar months. M1 starts 6 April, so any pay date 6 April through 5 May falls in M1, regardless of whether your payroll calls that "April" or "May" pay.

How tax months drive PAYE

HMRC's PAYE system applies cumulative tax codes by tax month. At each pay date, the employer calculates:

Year-to-date pay = sum of pay through tax month X.
Year-to-date allowance = (PA / 12) × X (e.g. M3 → 3 × £1,047.50 = £3,142.50).
Year-to-date taxable income = YTD pay − YTD allowance.
Year-to-date tax due = apply bands to YTD taxable.
This month's tax = YTD tax due − YTD tax already paid.

This system self-corrects fluctuations: a high-bonus month is followed by a low-bonus month and the tax averages out. Only emergency codes (W1, M1, X) suspend the cumulative logic.

Statutory pay (SSP, SMP, etc.) uses tax weeks rather than tax months. SMP runs 39 weeks; SSP runs up to 28 weeks. Tax months are used for monthly-paid employees and for reporting to HMRC via Real Time Information (RTI) by tax-month end.

Three worked examples (UK 2025/26)

Example 1: Pay date 25 April 2025

25 April 2025 falls in tax month 1 (M1), tax year 2025/26.

Example 2: Pay date 5 May 2025

5 May 2025 — last day of M1.

Example 3: Pay date 6 May 2025

6 May 2025 — first day of M2 (tax month 2).

Common mistakes to avoid

Assuming tax month = calendar month — they're offset by 5 days.
Treating bonus paid 6 April as part of prior tax year — it's M1 of new year.
Confusing tax weeks with tax months — both exist; weekly payroll uses W1-52, monthly uses M1-12.
Forgetting that a 53rd tax week occasionally occurs in some years (when 5 April lands on certain weekdays).
Setting up monthly direct debits on 6th and treating it as 'this month's' tax — actually crosses into the new tax month.

When to use this calculator

Use this calculator when you need to identify the tax month of a specific pay date — important for cumulative PAYE reconciliation, RTI submissions, or determining when statutory pay periods began. Useful for payroll administrators, accountants, and employees verifying their tax codes mid-year.

Regional differences (Scotland, Wales, Northern Ireland)

Tax months are UK-wide and identical in England, Scotland, Wales, and Northern Ireland. Devolved income tax bands (Scottish/Welsh) apply within the same M1-M12 tax-month structure. PAYE software handles all four nations uniformly.

UK Tax Month Calculator — 2025/26 PAYE

UK tax year date calculator