Calendar
A clear month and year calendar with week numbers and date maths.
January 2026
Today
Thursday, January 1, 2026
Today
ISO week
1
Day of year
1
Days left in year
364
Quarter
Q1
Days between two dates
Dates are counted, not estimated. Gaps are worked out from calendar days rather than by adding hours, so daylight-saving changes and leap years do not shift the answer by a day. Week numbers follow ISO-8601, the standard used across Europe and in most business software: weeks start on Monday and week 1 is the one containing the first Thursday of the year.
Private by design. This tool runs entirely in your browser. Your input is processed on your own device and is not uploaded by DO101.
About the Calendar
See any month or a whole year at a glance, with ISO week numbers down the side and today marked. Click a date for its week number, day of the year, quarter and how far away it is, and work out the gap between any two dates in days, weeks or working days.
How to use it
- 1Browse months with the arrows, or switch to the whole-year view.
- 2Click any date to see its week number, day of the year and quarter.
- 3Choose whether your week starts on Monday or Sunday.
- 4Use the date range boxes to count days, weeks or weekdays between two dates.
What you get
- Month view and a full twelve-month year view
- ISO-8601 week numbers, the standard used across Europe
- Day of the year, days remaining and calendar quarter
- Days, weeks and working days between any two dates
- Monday or Sunday week start
- Counted in calendar days, so daylight saving never shifts the answer
Frequently asked questions
How are week numbers calculated?
By ISO-8601: weeks start on Monday, and week 1 is the week containing the first Thursday of the year. This is the standard used across Europe and in most business software, and it can differ from the US convention by a week.
Why does the days-between count sometimes differ from other tools?
Some tools count the gap and some count both end dates. This one gives the gap — from Monday to Tuesday is one day. The working-days figure counts both ends inclusively, which is how leave is usually booked.
Does it handle leap years and daylight saving?
Yes. Dates are compared as calendar days rather than by adding 24-hour blocks, which is what causes off-by-one errors around clock changes. February 29 is handled correctly, and the tool tells you whether the year you are looking at is a leap year.
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