Date calculator
Pick a start date, choose add or subtract, and say how many years, months, weeks and days. The answer is the date with its weekday, and how far it is from the start and from today.
How it works
The calculator starts from the date you pick, which begins as today. It adds or takes away the years and months first, and then the weeks and days, at 7 days to a week.
Months need a rule, because they have different lengths. When the month you land in is too short for the day, the answer is that month’s last day. One month after January 31, 2026 is February 28, and one year after February 29, 2024 is February 28, 2025.
A worked example
Sunday, March 15, 2026 plus 90 days is Saturday, June 13, 2026, which is 12 weeks and 6 days after the start.
With several units at once, January 1, 2026 plus 2 years, 3 months, 2 weeks and 5 days is Thursday, April 20, 2028. The years and months reach April 1, 2028, and the 19 days after that reach the 20th.
Subtracting works backward in the same order. March 31, 2026 less 1 month and 1 day is Friday, February 27, 2026, because one month back is February 28 and the extra day is the 27th.
What it leaves out
The calculator counts calendar days, so it ignores hours, time zones and holidays, and a weekend counts like any other day. For working days, use the business days calculator. Dates run from the year 1 to the year 9999, and an answer outside them is refused. A lender or an office may count months in its own way, so for a deadline in a contract, ask whoever sets it.
Questions
How do I find the date 90 days from a date?
Add 90 days to the start date. From Sunday, March 15, 2026, 90 days is 12 weeks and 6 days, and the date is Saturday, June 13, 2026.
What is one month after January 31?
February has no 31st, so the calculator gives the last day of February: February 28, 2026. A month that is too short for the day always ends on its last day.
Does the calculator count the start day?
No. The start day is day 0, so one day after March 15 is March 16.
In what order are the years, months, weeks and days added?
The years and months go first and the weeks and days after. March 31, 2026 less 1 month and 1 day is February 27: one month back is February 28, and one more day is the 27th.
How do I count working days instead?
Use the business days calculator. It leaves out weekends and, if you choose, the US federal holidays.
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