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Date calculator
Count midnights between two dates, or add a whole number of days. 2026-01-01 to 2026-01-11 is 10 days. The day after 2024-02-28 is 2024-02-29. Dates stay in this browser.
Why this exists
The age calculator counts years, months, and days from a birthday. This page only counts a gap or shifts a date.
Counting both ends is one more than the gap. From 1 January through 11 January, the question of how many days splits into 10 or 11.
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01How to use it
On Between, type the two dates. Today fills the start with this device’s date.
On Add days, type a start date and a whole number of days. A negative number moves backward.
Copy puts the large line, the weeks, the count of both dates, and the weekdays on the clipboard. Closing the tab clears the dates.
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02What you get
2026-01-01 to 2026-01-11 is 10 days later, 1 week and 3 days, and 11 dates if both ends count. Thursday goes to Sunday.
2024-02-28 to 2024-03-01 is 2 days. 2023-02-28 to 2023-03-01 is 1 day. 2024-01-01 plus 366 days is 2025-01-01.
Entered2026-01-01 → 2026-01-11
2026-01-01 → 2026-01-11 10 days later · 1 week and 3 days · both dates 11 2024-02-28 → 2024-03-01 2 days 2023-02-28 → 2023-03-01 1 day 2024-02-28 + 1 2024-02-29 -
03Worth knowing
This page is not an age. Years, months, and days from a birthday belong on the age calculator.
2026-01-11 to 2026-01-01 is 10 days earlier. Reversing the dates changes the sign.
The weekday comes from the calendar date alone. Sunday is 0.
Counting the same day at both ends makes 1. The gap is 0.
Questions
- QIs 2026-01-01 to 2026-01-11 ten days or eleven?
- AThe gap is 10 days. Counting both dates makes 11.
- QIs the day after 2024-02-28 the 1st of March?
- ANo. 2024 is a leap year, so the next day is 2024-02-29. The next day after 2023-02-28 is 2023-03-01.
- QWhat if the end is earlier than the start?
- AThe line says 10 days earlier. The sum does not stop.
- QAre the dates saved?
- ANo. They stay in this browser and are not sent to a server.
How this page works it out
This page counts the midnights from the start date to the end date. The start date is day 0. From 2026-01-01 to 2026-01-11 the gap is 10 days, which is 1 week and 3 days. Counting both dates makes 11. The start is a Thursday and the end is a Sunday.
The reverse uses the same gap with the opposite sign. From 2026-01-11 to 2026-01-01 the line says 10 days earlier. The same day is a gap of 0, and counting both ends makes 1. The day after 2024-02-28 is 2024-02-29 because 2024 is a leap year. The day after 2023-02-28 is 2023-03-01. From 2024-02-28 to 2024-03-01 is 2 days, and from 2023-02-28 to 2023-03-01 is 1 day. 2024-01-01 plus 366 days is 2025-01-01.
A date that does not exist, such as 31 April, is refused. The day count is a whole number from -365000 to 365000, and a result outside the years 1 to 9999 stops. The weekday comes from the date alone, and Sunday is 0. This page does not split a birthday into years, months, and days. A date has no clock, so no time zone is added. The dates stay in this browser and are not sent to a server.