Date Duration Calculator
Calculate the duration between two dates or add/subtract days, weeks, months, and years from a date. Includes business-day count.
A flexible date calculator with two modes: (1) compute the exact duration between two dates in years, months, days, weeks, hours, minutes, and business days; (2) add or subtract any number of days, weeks, months, or years from a starting date. Handles month-end edge cases (e.g., Jan 31 + 1 month = Feb 28/29) correctly. Everything runs locally in your browser.
Working with dates is surprisingly tricky — months vary in length, leap years happen, and "one month from January 31" doesn't land on a real date. Our Date Duration Calculator handles all of this for you. In Duration mode, enter two dates and get an exact breakdown in years, months, and days, plus totals in weeks, days, hours, and minutes, and a business-day count (Mondays through Fridays) for workday planning.
In Add/Subtract mode, pick a starting date, type an amount, choose a unit (days, weeks, months, or years), and set the direction. The tool computes the resulting date, correctly clamping month-end overflows: January 31 plus one month becomes February 28 (or 29 in a leap year), not "February 31". Useful for deadlines, contract terms, due dates, project planning, and any situation where you need precise date math without spreadsheet gymnastics.
- 1
Pick a mode
Choose Duration to measure between two dates, or Add/Subtract to shift a date forward or backward by a unit of time.
- 2
Enter the dates and values
Use the native date pickers to select dates. For add/subtract, choose the amount, unit (days/weeks/months/years), and direction.
- 3
Read the results
Duration mode shows a full breakdown with business days. Add/Subtract mode shows the resulting date with day of week and ISO format.
Project deadlines
Calculate when a 90-day or 6-month project milestone lands — and whether it falls on a weekend.
Contract and rental terms
Determine end dates for leases, contracts, or subscriptions that run for a specific duration from a start date.
Count working days
Plan project capacity or PTO by counting only Mondays through Fridays between two dates.
Anniversary and milestone planning
Figure out exactly how many days, weeks, or months until (or since) an important event.
How are months and years calculated?
In Duration mode, the difference is computed calendar-style: years first, then months, then days, with borrowing when needed (similar to how you'd compute someone's age). In Add/Subtract mode, adding months or years shifts the month/year field directly and clamps the day if the target month is shorter.
What happens for edge cases like Jan 31 + 1 month?
The result is clamped to the last valid day of the target month. Jan 31 + 1 month becomes Feb 28 (or Feb 29 in a leap year). This matches how most calendar apps and financial systems handle it.
Are business days adjusted for holidays?
No — the business day count only excludes Saturdays and Sundays. Public holidays are not deducted because they vary by country and region.
Does it work if the end date is before the start date?
Yes. Duration mode shows the absolute difference and flags that the dates are reversed so you're aware.
Is any data sent to a server?
No. All date calculations run entirely in your browser. Nothing is transmitted anywhere.