Week number · ISO 8601, US and UK tax weeks
It is week 40 of 2026
Today, Monday 28 September 2026, is in ISO week 40 of 2026, which runs from Monday 28 September 2026 to Sunday 4 October 2026. On the US-style count, with Sunday starts and week 1 as the week containing 1 January, it is week 40. In UK payroll it is tax week 26 and tax month 6 of the 2026/27 tax year.
ISO week
40
of 53 in 2026
US-style week
40
Sunday start
UK tax week
26
2026/27 tax year
UK tax month
6
from 6 April
Day of the year
271
Monday
ISO week 40: Monday 28 September 2026 to Sunday 4 October 2026.
US-style week 40: Sunday 27 September 2026 to Saturday 3 October 2026.
Updated daily; counted from Monday 28 September 2026.
How ISO 8601 week numbers work
ISO 8601 weeks start on Monday, and week 1 is the week that contains the year's first Thursday, which is the same as the week containing 4 January. A year has 53 ISO weeks when it starts on a Thursday, or on a Wednesday in a leap year. 2026 has 53 ISO weeks. ISO week numbers are the standard in the UK and Europe and in most diaries and software set to a UK locale.
Why US week numbers can differ
Many US calendars and the default WEEKNUM setting in spreadsheets start weeks on Sunday and count the week containing 1 January as week 1, however few days of it are in January. This year 1 January was a Thursday, so the two counts give the same number today, week 40. Check which system a colleague or client uses before quoting a week number.
UK tax week and tax month
According to the Income Tax (PAYE) Regulations 2003, tax week 1 runs from 6 to 12 April and each tax month runs from the 6th to the 5th, so tax month 1 is 6 April to 5 May. Today is in tax week 26 and tax month 6, which began on 6 September 2026. Payroll uses these numbers for cumulative tax codes, and the salary pages show what each month's pay looks like after tax.
This week's dates and week numbers
The ISO week runs Monday to Sunday. The US-style number changes on Sunday, so Sunday shows the next US week.
| Day | Date | ISO week | US-style week |
|---|---|---|---|
| Monday | 28 September 2026 | 40 | 40 |
| Tuesday | 29 September 2026 | 40 | 40 |
| Wednesday | 30 September 2026 | 40 | 40 |
| Thursday | 1 October 2026 | 40 | 40 |
| Friday | 2 October 2026 | 40 | 40 |
| Saturday | 3 October 2026 | 40 | 40 |
| Sunday | 4 October 2026 | 40 | 41 |
The next 8 ISO weeks
Each ISO week with its Monday start and Sunday end.
| ISO week | Starts | Ends |
|---|---|---|
| Week 41 (2026) | Mon 5 Oct 2026 | Sun 11 Oct 2026 |
| Week 42 (2026) | Mon 12 Oct 2026 | Sun 18 Oct 2026 |
| Week 43 (2026) | Mon 19 Oct 2026 | Sun 25 Oct 2026 |
| Week 44 (2026) | Mon 26 Oct 2026 | Sun 1 Nov 2026 |
| Week 45 (2026) | Mon 2 Nov 2026 | Sun 8 Nov 2026 |
| Week 46 (2026) | Mon 9 Nov 2026 | Sun 15 Nov 2026 |
| Week 47 (2026) | Mon 16 Nov 2026 | Sun 22 Nov 2026 |
| Week 48 (2026) | Mon 23 Nov 2026 | Sun 29 Nov 2026 |
Guides and definitions
- How much notice do I need to cancel a contract or subscription? (Guide)
- Cooling-off period (A cooling-off period is the 14 days UK law gives you to cancel most contracts made online, by phone or off-premises, without a reason.)
- Notice period (A notice period is the time between telling the other party you are ending a contract and the date it actually ends.)
More date answers
- Days left in the year (94 days)
- 6 weeks from today (9 Nov 2026)
- 2 weeks from today (12 Oct 2026)
- Days until Christmas (25 Dec 2026)
Every countdown · Every day and week from today · Salary after tax by month · Count working days this week
Common questions
What week number is it today?
Today, Monday 28 September 2026, is in ISO week 40 of 2026, from Monday 28 September 2026 to Sunday 4 October 2026. On the US Sunday-start count it is week 40.
How many weeks are there in 2026?
2026 has 53 ISO weeks. A year has 53 ISO weeks when 1 January is a Thursday, or a Wednesday in a leap year; 1 January 2026 was a Thursday. Week 53 ends on Sunday 3 January 2027.
When does week 1 of next year start?
ISO week 1 of 2027 starts on Monday 4 January 2027, the Monday of the week that contains 4 January.
What tax week is it in the UK?
Today is tax week 26 and tax month 6 of the 2026/27 tax year. The tax year starts on 6 April, tax week 1 is 6 to 12 April, and tax month 6 began on 6 September 2026.
Do week numbers start on Monday or Sunday?
ISO 8601, used in the UK and Europe, starts weeks on Monday. Many US calendars start on Sunday. Today the ISO count gives week 40 and the US count gives week 40, and the two can differ by one for part or all of the year.
Sources and assumptions
- Week numbers are for today in the UK time zone and refresh in your browser for your own date.
- The US-style count is a common convention, not a standard: weeks start on Sunday and week 1 contains 1 January.
- ISO: ISO 8601 date and time format
- legislation.gov.uk: Income Tax (PAYE) Regulations 2003, regulation 2 (tax week and tax month)
Dates are worked out for the UK time zone and refreshed in your browser for your own date. Your employer, court or contract may count days differently, so check the exact rule that applies to you.