Date Calculator
Add or subtract days, weeks, months, or years from a date.
Try an example
Saturday, January 31, 2026
About this calculator
What Is a Date Calculator?
A date calculator does two jobs: it tells you how much time lies between two dates, and it adds or subtracts a span of time from a date to find a new one. Use it to count the days until a deadline or vacation, to find out what date falls 90 days after an invoice, to work out how long a project ran, or to see what day of the week a particular date lands on. The result can be given in years, months, weeks and days.
Days Between Two Dates
Pick a start and end date and the calculator returns the exact gap. Whether the end date itself is included changes the answer by one day, so decide in advance how your situation counts — a hotel stay from the 1st to the 5th is four nights, but a conference running the 1st through the 5th covers five days. For counting only the days and getting a quick total, the Day Counter is a lighter alternative.
Worked Example
Adding 90 days to January 1, 2026 lands on April 1, 2026, a Wednesday.
Adding or Subtracting Time
Start from a date and add or subtract years, months, weeks or days to find another. Months are the tricky part, because they differ in length: adding one month to January 31 has no matching "February 31," so tools usually land on the last day of February. Be aware of that edge case when scheduling things like billing dates and lease terms.
A Short History of the Calendar
Most of the world uses the Gregorian calendar, in which a standard year has 365 days and an extra day is added to February in leap years. April, June, September and November have 30 days; February has 28 or 29; the rest have 31. It reformed the older Julian calendar, which itself grew out of the ancient Roman calendar — originally a lunar calendar that struggled to stay aligned with the seasons. The Gregorian rules drop three leap days every 400 years, which keeps calendar dates in step with the solar year.
Leap Years in One Rule
A year is a leap year if it is divisible by 4, except for century years, which must be divisible by 400. So 2024 and 2000 are leap years, while 1900 and 2100 are not.
Related Tools
To measure a person's age precisely, use the Age Calculator; for hours and minutes, the Time Calculator and the Time Duration Calculator; and for pregnancy dates, the Due Date Calculator.
Worked example
Adding 30 days to January 1, 2026 lands on January 31, 2026.
Frequently asked questions
Does adding months keep the same day of the month?
Usually — adding 1 month to January 31 would land on a date that doesn't exist in February, so the calendar automatically rolls it forward to the nearest valid date (e.g., March 2 or 3, depending on the month lengths involved).
Does this account for leap years?
Yes — all date arithmetic uses actual calendar dates, so February's length and leap years are handled automatically rather than assuming a fixed number of days per month or year.
Can I calculate a date in the past?
Yes — choose "Subtract" to count backward from the start date instead of forward.
