This week
Week 19
The current ISO week runs from Monday, May 4, 2026 through Sunday, May 10, 2026.
Quick reference: May 4 to May 10.
ISO Week Number
The current ISO 8601 week number is 19 of 2026. ISO weeks start on Monday, end on Sunday, and week 1 is the week containing the year's first Thursday.
Current ISO year
ISO week numbering can cross the regular calendar year boundary. Late December dates can fall into week 1 of the next ISO year, and early January dates can belong to the last ISO week of the previous one.
For today, the active ISO year is 2026.
How ISO weeks are calculated
Core rules
- Week 1 is the week containing the first Thursday of January.
- Weeks always start on Monday and end on Sunday.
- Every ISO week has exactly 7 days.
- Years can have 52 or 53 ISO weeks.
Why people use them
- Project schedules and manufacturing calendars
- Payroll, accounting, and reporting periods
- Transport, warehousing, and logistics planning
- International teams that work across countries with different local date conventions
How many weeks are in a year?
Most ISO years contain 52 weeks. Some contain 53. A 53-week ISO year happens when January 1 falls on a Thursday, or when it falls on a Wednesday in a leap year.
| ISO year | Weeks | Notes |
|---|---|---|
| 2024 | 52 | Standard 52-week ISO year |
| 2025 | 52 | Standard 52-week ISO year |
| 2026 | 53 | Includes week 53 |
| 2027 | 52 | Standard 52-week ISO year |
| 2028 | 52 | Standard 52-week ISO year |