Last updated: March 2026
Calculating Time Between Dates
Date arithmetic sounds simple until you actually try to do it. Months have different lengths, leap years add a day, and business day counting requires tracking holidays. This calculator handles all of these correctly so you don't have to count on your fingers.
The average American works approximately 251 business days per year, making business day calculations essential for project planning and deadline management.
The "Days Between" mode gives you the exact count in multiple formats — total days, years/months/days, weeks, hours, and minutes. The "Include end date" toggle is important: counting days for a hotel stay or rental period usually includes both the check-in and check-out dates.
The "Add/Subtract" mode answers questions like "what date is 90 days from today?" — common for contract deadlines, project timelines, pregnancy due dates, and warranty expirations. You can add days, weeks, months, or years, and subtract just as easily.
Business days mode is essential for legal deadlines, shipping estimates, and project planning. It excludes weekends and optionally excludes US federal holidays. The mini calendar view gives you a visual overview of which days count.
Frequently Asked Questions
How does the date calculator work?
Enter two dates to find the exact number of days between them, broken down into years, months, weeks, and days. You can also add or subtract days from any date, or calculate business days excluding weekends and holidays.
Does it handle leap years?
Yes. The calculator uses JavaScript's built-in Date object which correctly handles leap years, including the edge cases of February 29th calculations and century leap year rules.
What counts as a business day?
Business days are Monday through Friday, excluding weekends. When 'Exclude US holidays' is checked, 10 federal holidays (New Year's, MLK Day, Presidents' Day, Memorial Day, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving, Christmas) are also excluded.
Can I include the end date in the count?
Yes. Toggle 'Include end date in count' to add 1 to the total. This is useful when both the start and end dates should be counted (e.g., rental days, event durations).
How do I add months to a date?
Switch to 'Add/Subtract Days' mode, enter your date, set the amount, and select 'Months' from the unit dropdown. The calculator handles month-end edge cases (e.g., adding 1 month to January 31 gives February 28).