The Date Calculator computes the difference between two dates in various time units — days, weeks, months, years, and hours.
Also calculates the number of working days (Monday-Friday) and can be used to find a date after adding/subtracting a number of days. Useful for deadlines, due dates, document expiry, and project planning.
Calculator information
📋 How to use this calculator
- Choose a mode: Difference between two dates, Add days to a date, or Subtract days from a date.
- Enter the start date and end date (for difference mode) or a reference date plus the number of days.
- Enable the business-day option if you want to skip Saturdays and Sundays.
- Check the federal holidays option for a more accurate effective workday count.
- Click Calculate to see results in multiple units: years, months, weeks, days, hours, minutes.
- Use the result for planning deadlines, due dates, validity periods, or event countdowns.
🧮 Date Difference and Day Addition
Difference = |End Date - Start Date|; New Date = Start Date ± N days
- Difference in days = Julian Day End - Julian Day Start
- Business Days = Total days - count of Saturdays, Sundays, and federal holidays
- 1 week = 7 days, 1 month average = 30.44 days, 1 year = 365.25 days (accounting for leap years)
- Leap year: divisible by 4, except century years which must be divisible by 400
- Input format supports MM/DD/YYYY or YYYY-MM-DD
The Gregorian calendar (1582-present) is used; earlier dates follow the Julian calendar with different rules.
💡 Worked example: Calculating the difference from January 1, 2026 to December 31, 2026
Given:- Start date = January 1, 2026
- End date = December 31, 2026
- 2026 is not a leap year (2024 was, 2028 will be)
Steps:- Total days = 365 - 1 = 364 days (excluding the start date)
- Or inclusive of both dates = 365 days
- Conversion: 364 / 7 = 52 weeks
- Conversion: 364 / 30.44 = 11.96 months
- Business days (Mon-Fri): 261 days in calendar year 2026
- Minus 11 U.S. federal holidays in 2026 = 250 effective workdays
Result: A difference of 364 days or 52 weeks, consisting of 261 weekdays - 11 federal holidays = 250 effective workdays.
❓ Frequently asked questions
How many effective workdays are there in a U.S. calendar year?
A year has 365 days (366 in a leap year). After subtracting 104 Saturdays and Sundays, 261 weekdays remain. The U.S. federal government observes 11 federal holidays per year (per 5 U.S.C. § 6103). Private-sector employers typically grant 6-11 paid holidays plus 10-15 PTO days, giving roughly 235-245 effective workdays. State and local holidays can add to or shift this count.
Is 2026 a leap year?
2026 is NOT a leap year. A leap year (366 days) is one divisible by 4 (2024, 2028), except century years, which must be divisible by 400 (1900 was not a leap year, 2000 was). Leap years contain February 29. Pattern: 2024 leap, 2025-2027 regular, 2028 leap, and so on. The leap-year rule corrects the Julian calendar to align with Earth's orbital period of 365.2425 days/year.
How do I calculate a loan or document due date?
For a loan due date, add the term length (days, months, or years) to the disbursement date. For example, a 12-month loan disbursed on May 13, 2026 matures on May 13, 2027. For documents with a fixed validity period (driver's license, passport), validity is counted from the issue date. Always check the printed expiration date and set a 30-day reminder ahead of expiration.
What's the difference between calendar days and business days in a contract?
Calendar days include every day - Saturdays, Sundays, and holidays. Business days are Monday-Friday only, excluding federal (and sometimes state) holidays. Under the Federal Rules of Civil Procedure (Rule 6), periods of less than 11 days exclude weekends and holidays; longer periods count calendar days. SLAs, payment terms, and rescission notices typically specify 'business days' explicitly. '7 days' = 7 calendar days; '7 business days' may span 9-11 calendar days.
Why do results differ from other calculators?
Differences usually come from inclusive vs. exclusive counting. Inclusive: both endpoints count (Jan 1 to Jan 3 = 3 days). Exclusive: the start date is not counted (= 2 days). ISO 8601 and this calculator default to exclusive counting. Time-zone differences can also create a one-day offset, especially around midnight transitions. For consistency, use your local time zone throughout.
📚 Sources & references
Last updated: May 11, 2026