Two calculators in one
Days between dates counts the time from a start date to an end date and shows it as total days, weeks and days, years, months and days, total months, and the number of weekdays and weekend days. Add or subtract takes a start date and moves it forwards or backwards by a number of days, weeks, months or years, and shows the resulting date and day of the week.
Counting days between dates
By default the calculator counts the number of days you must move forward to get from the start date to the end date — so from Monday to the following Monday is 7 days. This is how most deadlines and durations are measured. If you are counting days of an event that includes both the first and last day — for example a holiday from the 1st to the 7th is 7 days long — tick Include the end date, which adds one day.
Example: from January 1, 2026 to December 25, 2026 is 358 days — 51 weeks and 1 day, or 11 months and 24 days.
Adding and subtracting months and years
Adding days and weeks is simple arithmetic, but months and years have different lengths. The calculator moves to the same day number in the target month; if that day does not exist (for example February 30), it uses the last day of the month and tells you. Adding one year to February 29 gives February 28 in a non-leap year.
Useful during pregnancy and parenthood
- How many days since your last period? Count from that date to today — or use the Pregnancy Week Calculator, which converts it into weeks pregnant.
- Planning leave: add weeks to a start date to find the return date.
- Counting down: how many days until your due date? The Days Until Due Date Calculator does this automatically.
- Baby’s age: count from the birth date, or use the Baby Age Calculator for weeks, months and milestones.
Leap years and calendars
All calculations use the standard Gregorian calendar and count whole calendar days, so leap years — every four years, except century years not divisible by 400 — are always taken into account. 2028 is the next leap year, with a February 29.