Date Calculator: Add or Subtract Years, Months and Days
Move a date forward or back by years, months, weeks and days, or find the time between two dates in years, months and days. One month after January 31 is February 28, or February 29 in a leap year, and the answer is the same in every time zone.
How to use the Date Calculator
- Choose Add or Subtract to move a date, or Time Between Dates to measure the time from one date to another.
- To move a date, pick the start date, choose + Add or − Subtract and fill in the years, months, weeks and days. A blank box counts as 0. Press Calculate Date.
- To measure the time between two dates, pick the start and end dates and press Calculate Difference.
How the dates are worked out
New date = start date ± (years × 12 + months) calendar months, then ± (weeks × 7 + days) days · · · Time between = whole years, then whole months, then the days left
The calculator works on calendar dates and never on clock times, so neither your time zone nor a daylight saving change can move a result by a day. Years and months go first. A year is 12 months, and a month keeps the day of the month, so March 15 plus 1 month is April 15. When the new month has no such day, the result is its last day. January 31 plus 1 month is February 28, or February 29 in a leap year. January 31 plus 2 months is March 31, because the months count from the start date. Subtracting follows the same rule, so March 31 minus 1 month is February 28. Weeks and days go last, at 7 days to a week. Time Between Dates runs the rule the other way. A whole month has passed each time the day of the month of the start date comes around again, or the last day of a month too short for it. The days after the last whole month are the remainder.
Worked example
Start on October 17, 2026 and add 1 year, 6 months, 2 weeks and 3 days. The 18 months come first and land on April 17, 2028. The 17 days after that give Thursday, May 4, 2028. In Time Between Dates, March 15, 1990 to May 26, 2026 is 36 years, 2 months and 11 days. That is 13,221 days, or 1,888 whole weeks.
Frequently asked questions
What is January 31 plus 1 month?
February 28, or February 29 in a leap year. February has no 31st, so the calculator stops on its last day. The spare days do not spill over into March. Add 2 months to January 31 and you get March 31, because every month counts from the start date.
In what order are years, months, weeks and days added?
Years and months first, then weeks and days. The order matters near the end of a month. January 30, 2026 plus 1 month and 1 day is March 1. The month gives February 28, and the day after that is March 1. Adding the day first would give January 31 and then February 28.
How is the time between two dates counted?
In whole years, then whole months, then days. The start date counts and the end date does not, so Monday to Tuesday is 1 day. A whole month has passed each time the day of the month of the start date comes around again. If a month has no such day, its last day stands in, so January 31 to February 28, 2026 is 1 month. The Days and Weeks boxes show the same span as totals.
Where can I count only the days between two dates?
In the day counter. It counts the days between two dates, with an option to include the end date, and splits them into weeks, months and weekdays. It also adds or subtracts a number of days. This page moves a date by years and months too, which the day counter does not.
Are leap years handled?
Yes. February 29 exists in 2024 and 2028, and in 2000, but not in 1900 or 2100. February 29, 2024 plus 1 year is February 28, 2025. Plus 4 years it is February 29, 2028.
Does my time zone change the answer?
No. The calculator reads the dates you pick as calendar days and does all of its arithmetic on them, never on clock times. A daylight saving change inside the span adds or drops nothing, and each date shows the same weekday wherever you are.