Calculate the duration between two dates, or add/subtract days, weeks, months, or years to a specific base date. Get detailed statistics, business days, and time breakdowns.
Our standard Gregorian calendar features months ranging from 28 to 31 days. Additionally, **Leap Years** add an extra day to February (29 days) once every four years to keep our calendar aligned with the Earth's astronomical revolution around the Sun (which takes approximately 365.2422 days).
Our calculator accounts for exact Gregorian calendar rules, including century boundary overrides (years divisible by 100 are not leap years unless also divisible by 400), ensuring calculations across year boundaries are perfectly precise.
When tracking sprint boundaries, milestone deadlines, or shipping durations, projects typically rely on **Business Days** (which omit Saturday and Sunday weekends) rather than total calendar days.
The sidebar breakdown automatically provides this count, allowing you to estimate operational work effort accurately without manual tallying.
Prior to 1582, the western world used the Julian Calendar introduced by Julius Caesar. However, it overestimated the solar year by about 11 minutes per year. By the 16th century, the calendar had drifted 10 days out of alignment with the solar seasons. To correct this, Pope Gregory XIII introduced the Gregorian calendar. When countries adopted the new system, they had to skip days: in October 1582, the day after Thursday, Oct 4 was Friday, Oct 15! Our calculator operates on the standardized modern Gregorian rules retroactively for simplicity and programming uniformity.
Subtracting dates manually is similar to subtracting numbers with carrying. For example, if you want to find the duration from **March 15, 2026** to **June 5, 2026**: