Weekstamp

One day · two calendar labels

Keep the week with its year.

Convert a Gregorian date to its ISO week-date label, or decode an ISO week date into its calendar day. Weekstamp makes year boundaries and Monday-to-Sunday endpoints explicit.

Date-only, proleptic Gregorian years 0001–9999. No timezone, device clock or custom business-week scheme.

Choose a date label

Use four year digits, two month digits and two day digits, separated by hyphens. Example: 2021-01-01.

Week 1 contains January 4, equivalently the year’s first Thursday. A year has 52 or 53 ISO weeks. Read the accepted formats and bounds.

Keep the current conversion

Copy and local downloads include both labels, the week-year and available week endpoints. Editing either field or changing mode clears old output until you convert again.

Monday comes first

ISO weekdays run Monday 1 through Sunday 7. This differs from week numbering that starts on Sunday or has a week zero.

The week-year can change

2021-01-01 belongs to 2020-W53-5. Keep the ISO week-year with its week number instead of borrowing the calendar year.

No instant is inferred

A civil date label has no time of day or timezone here. The tool does not turn it into a timestamp or determine your local date.