Date Calculator
Do date arithmetic two ways: count the exact time between two dates (in calendar days or business days), or add and subtract years, months, weeks and days from a starting date. Leap years, month lengths and US federal holidays are all handled correctly.
Two kinds of date arithmetic
The "days between" mode counts the exact number of days from one date to another and also expresses that span in weeks, in calendar years/months/days, and in hours and minutes. The "add or subtract" mode starts from a date and moves forward or backward by a combination of years, months, weeks and days, returning the resulting date together with its weekday name. Both modes handle month lengths, leap years and year boundaries automatically.
Calendar days versus business days
By default the calculator counts every calendar day, including weekends and public holidays. That is the right basis for anniversaries, plain deadlines, or measuring how long ago something happened. Switch the "Count which days?" option to "Business days" to skip Saturdays and Sundays, useful for shipping estimates and working-day contractual deadlines. The third option also excludes the 11 main US federal holidays (New Year's Day, MLK Day, Presidents' Day, Memorial Day, Juneteenth, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving, and Christmas).
Include the end day
The default behaviour counts the gap between the two dates: from January 1 to January 3 is 2 days. Turn on "Include the end day" to count both endpoints: January 1 to January 3 becomes 3 days. This matters for legal and billing contexts where both the first and last days are chargeable or enforceable.
Adding a mix of years, months, weeks and days
In add/subtract mode you can combine any of the four units at once. For example, adding 1 year, 2 months and 15 days to a date applies the year increment first (adjusting for leap years if needed), then the months (adjusting for month lengths), and finally the days. This matches the way human calendars work rather than simply converting everything to a raw day count.
How the three day-counting modes differ
| Mode | Skips weekends | Skips US holidays | Best for |
|---|---|---|---|
| All calendar days | No | No | Anniversaries, event countdowns, age calculations |
| Business days | Yes | No | Shipping estimates, general working-day deadlines |
| Business days excl. holidays | Yes | Yes | US legal notices, HR payroll periods, court filings |
Use this to pick the right setting for your situation.
Frequently asked questions
Does the count include the start and end date?
By default it counts the gap between the two dates, so January 1 to January 3 is 2 days. Turn on the "Include the end day" toggle to count both endpoints, making January 1 to January 3 equal 3 days. Use inclusive counting for legal, billing or scheduling contexts where both the first and last day are counted.
Are leap years handled correctly?
Yes. The day count includes February 29 whenever a leap year falls in the range, and the years/months/days breakdown respects each month's true length. The add/subtract mode also handles the edge case of adding months to a date like January 31 (it clips to the last valid day of the destination month).
How are business days calculated?
Business day counting iterates through every calendar day in the range and skips Saturdays and Sundays. The "excl. US holidays" option additionally skips the 11 main federal holidays (New Year's Day, MLK Day, Presidents' Day, Memorial Day, Juneteenth, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving, and Christmas). Floating holidays are pinned to their most common calendar date.
Can I add months and days together?
Yes. In the add/subtract mode, fill in any combination of years, months, weeks and days. The calculator applies the increments in order: years first, then months, then the combined week and day total. This mirrors how human calendars work and avoids the errors that come from converting months to a fixed number of days.
Can I calculate backward in time?
Yes, two ways. In "days between" mode the order of the two dates does not matter; the result is always the positive span. In "add or subtract" mode, choose "Subtract (go back)" to move to an earlier date.
Why do I get a different answer in hours versus days?
The hours and minutes outputs use the same calendar-day count, multiplying it by 24 or 1,440 respectively. They assume whole days with no time-of-day component. If your start and end times fall mid-day, the actual elapsed hours may differ by up to 24 hours from the displayed figure.