Week Number Calculator
Enter a date to see its week number, or enter a week and a year to see the dates that week covers.
Deze inhoud is in het Engels.
Week for a date
Dates for a week
Uitgewerkte voorbeelden
ISO week for mid October
Date 15 October 2026
Week 42 of 2026.
Weeks run from Monday to Sunday, and week 1 is the week containing the first Thursday of the year.
Early January date
Date 1 January 2027
Week 53 of 2026, since 1 January 2027 falls in the last week of 2026.
Some years have 53 weeks, so a date early in January can belong to the final week of the previous year.
Over Week Number Calculator
A week number calculator tells you which week of the year a date falls in. Many people need this for planning work rotas, school terms, project schedules, sprint cycles or payroll records that are filed by week. The standard system used across the United Kingdom and much of Europe starts each week on Monday and counts week one as the week that contains the first Thursday of January. This means the first few days of January can belong to the last week of the previous year, and the last days of December can belong to week one of the next year. Enter any date above to see its week number, the year that week belongs to and the exact Monday to Sunday dates it covers.
The second section works the other way round. If you know the week number and the year, for example week 12 of 2027, it shows the Monday and Sunday dates for that week and how many weeks the year contains. Some years have 53 weeks and most have 52, so the calculator checks that your week number is valid before it shows an answer. Use it to book a holiday, plan a delivery schedule, or check which dates a report covers. The results are written in plain English so they are easy to read on a phone or a computer.
Zo gebruikt u Week Number Calculator
- Pick a date in the first box to see its week number.
- Read the Monday and Sunday dates shown in the week runs line.
- To go the other way, type a week number from 1 to 53 in the second section.
- Enter the year, then read the dates that week covers.
- Check the weeks in the year line to confirm that the week exists.
Veelvoorkomend gebruik
- Planning shift rotas and holiday cover by week.
- Checking which week a report or invoice falls in.
- Setting school term or project sprint dates.
- Confirming the dates a delivery or appointment week covers.
Veelgestelde vragen
What is a week number?
A week number is the position of a week within the year. The most common system in the UK and Europe starts each week on Monday and counts week one as the week that contains the first Thursday of January. Most years have 52 weeks, and some have 53, so the week number on its own tells you where a date sits in the year.
Why does week 1 sometimes start in December?
Week one is the week that contains the first Thursday of January. Because of this, a few days at the start of January can belong to the last week of the previous year, and a few days at the end of December can belong to week one of the next year. This keeps every week a full block from Monday to Sunday, so no week is split across two different numbers.
How many weeks are in a year?
Most years have 52 weeks, but some have 53. A year has 53 weeks when it begins on a Thursday, or when it is a leap year that begins on a Wednesday. Years such as 2026 and 2032 have 53 weeks. Enter a year in the second section and the calculator will tell you how many weeks it contains, and it will refuse week numbers that do not exist.
Is the week number the same in every country?
No. Many countries, including the UK, most of Europe and Australia, use the Monday start system described here. The United States often uses a system where weeks start on Sunday, so week numbers can differ. If you need a week number for a contract, a school term or a project plan, check which system your organisation uses before you rely on the number.
How do I find the dates for week 20?
Type 20 in the week number box and the year in the year box. The calculator shows the Monday that starts that week and the Sunday that ends it. For example, week 20 of 2027 runs from Monday 17 May 2027 to Sunday 23 May 2027. The results also show how many weeks that year contains, so you can see whether a week 53 exists.