Week Number Calculator
Find the ISO 8601 week number for any date. See the day of the week and a visual calendar view of the entire week.
17
ISO Week
2026
Year
Wed
Day of Week
Week 17
Mon
Apr 20
Tue
Apr 21
Wed
Apr 22
Thu
Apr 23
Fri
Apr 24
Sat
Apr 25
Sun
Apr 26
How to Use the Week Number Calculator
- Enter the required date, time, or duration values.
- Select any additional options such as time zone or format.
- View the computed result instantly.
- Copy the result or adjust inputs as needed.
Riferimento Rapido
| Da | A |
|---|---|
| 1 minute | 60 seconds |
| 1 hour | 3,600 seconds |
| 1 day | 86,400 seconds |
| 1 week | 604,800 seconds |
| 1 year | 31,536,000 seconds |
| 1 year | 525,600 minutes |
Casi d'Uso
- •Tracking elapsed time for productivity or time management.
- •Setting precise intervals for cooking, exercise, or training.
- •Planning schedules and events across different time zones.
- •Calculating durations and deadlines for project management.
Formula
ISO 8601 defines week 1 as the week containing the first Thursday of the year. Weeks start on Monday. The week number is calculated by finding the nearest Thursday and counting weeks from January 1.
Domande Frequenti
What is the ISO 8601 week number?
ISO 8601 defines a standard way to number weeks. Week 1 is the week that contains the first Thursday of the year (equivalently, the week containing January 4). Weeks always start on Monday and end on Sunday.
How many weeks are in a year?
Most years have 52 weeks, but some years (called 'long years') have 53 weeks. A year has 53 ISO weeks if January 1 falls on a Thursday, or if December 31 falls on a Thursday.
Why do ISO weeks start on Monday?
The ISO 8601 standard chose Monday as the first day of the week to align with business practices in most countries. This differs from some locales (like the US) where Sunday is traditionally considered the first day.