Week Start Monday UTC
Choose a UTC calendar operation and enter a strictly formatted Gregorian date or time.
Enter a value to calculate locally.
Uses the proleptic Gregorian calendar, UTC arithmetic, and years 0001 through 9999. Input stays in this browser.
A QUICK WALKTHROUGH
How to use this tool
- Choose the UTC calendar operation.
- Enter the strict date or date-time value.
- Read the resulting UTC instant or seconds.
Strict Gregorian input
Enter the format required by the selected operation: week start uses YYYY-MM-DD; month boundaries use YYYY-MM; seconds since midnight uses YYYY-MM-DDTHH:mm:ss.
Bounded local calculation
Uses the proleptic Gregorian calendar, UTC arithmetic, and years 0001 through 9999. Input stays in this browser.
GOOD TO KNOW
Common questions
Is the input uploaded?
No. All calculations run locally in the browser.