How to use
Choose Days between dates for an exact whole-day difference, enter both dates, then calculate. A reversed range is shown with its direction.
Choose Add or subtract time, enter a starting date and nonnegative whole amounts, then select the operation.
Formula and calendar rule
Day difference = end date serial day − start date serial day. No clock, time zone, daylight-saving, weekend, or holiday rule is involved.
Calendar addition applies years, then months, then weeks and days. If a target month is shorter, the day is clamped to its last valid day; 2023-01-31 plus one month is 2023-02-28.
Examples and limits
From 2024-02-28 to 2024-03-01 is 2 days. Adding one year to 2024-02-29 gives 2025-02-28.
Years are limited to 0001–9999. This is a proleptic Gregorian calendar tool, not a business-day, holiday, historical calendar-transition, time-zone, or DST calculator.
Frequently asked questions
Is the end date included?
The difference treats the start as day 0, so equal dates are 0 days and the next date is 1 day later.
What happens at month end?
The day is kept when possible and otherwise clamped to the final valid day of the target month.
Does it count business days?
No. Every calendar day counts equally.