Week Number and Date Info
ISO week number, weekday, day of the year and quarter for any date.
Results
ISO week number
38
Day of the week
5
Day of the year
261
Number
3
Half of the year
2
Days
365
Leap year
No
What this tool does
Production planning, payroll and logistics often refer to a week number rather than a date, and the ISO rule is not obvious: week 1 is the one containing the first Thursday of the year. Weekday 1 is Monday and 7 is Sunday.
Formula
weekday · ISO week · day of the year · quarter
Variables
| Symbol | Meaning | Unit |
|---|---|---|
reference_date | Reference date | — |
week | ISO week number | — |
weekday | Day of the week | — |
day_of_year | Day of the year | — |
quarter | Number | — |
half | Half of the year | — |
days_in_year | Days | — |
LP | Leap year | — |
Worked example
- Reference date2026-09-18
- ISO week number38
- Day of the week5
- Day of the year261
- Number3
- Half of the year2
- Days365
- Leap yearNo
Limitations
- Dates are handled as calendar dates. Time zones, daylight saving changes and public holidays are not taken into account.