Day & Date Calculator
Calculate exact durations between dates, add or subtract calendar and business days to find future/past deadlines, and look up leap years and Julian days.
📆 Date Ranges
Duration📊 Time Calculation
Span ResultsUnderstanding Date & Time Calculations
Calendar Days vs. Business Days
**Calendar Days** count every single consecutive 24-hour period on the calendar, including weekends and holidays. **Business Days** represent only standard working days (Monday through Friday), skipping Saturday and Sunday. In project management, business days are essential for calculating contract deadlines, shipping intervals, and financial clearing schedules.
The Leap Year Rule
A leap year has 366 days instead of 365, adding February 29th to align the calendar year with the astronomical solar year. Under the Gregorian calendar rules, a year is a leap year if it is exactly divisible by 4, except for century years (ending in 00), which are only leap years if they are also exactly divisible by 400. E.g., 2000 was a leap year, but 1900 and 2100 are common years.
What is the Julian Day Number?
The **Julian Day Number (JDN)** is the integer number of days elapsed since the start of the Julian Period (January 1, 4713 BC). Astronomers and historical chronologists use this continuous fractional scale to calculate time elapsed between two distant events without having to deal with changes in calendar structures (such as switching from Julian to Gregorian dates).
A Worked Example
Counting from January 1, 2026 to March 1, 2026 spans 59 calendar days — January's 31 days plus February's 28, since 2026 isn't a leap year. If you only count business days, you exclude the weekends, leaving roughly 42 working days.
The tool also works in reverse: add 90 days to January 1, 2026 and you land on April 1, 2026 — handy for tracking a contract deadline, a 90-day return window, or a project milestone without counting on your fingers.
Frequently Asked Questions
How do I count the days between two dates?
Subtract the earlier date from the later one. You can choose whether to count both endpoints (inclusive) or only the gap between them — this tool shows the exact duration either way.
How many weeks are between two dates?
Divide the total number of days by 7. The calculator also breaks longer spans down into years, months, and days so you can read the duration however you need it.
How do I add or subtract business days?
Counting only Monday–Friday, the tool skips weekends as it adds or removes days — handy for shipping windows, contract deadlines, and payment terms that ignore weekends.