Date Difference Calculator

How day, month, and working-day counts work

Each date maps to a whole day number N on the Gregorian calendar, where Jan 1, 1970 is day 0. Subtracting N₁ from N₂ gives the exact day count with no time-zone or clock-change drift. From Jan 1, 2026 to Jul 4, 2026, that difference is 184 days (26 weeks, 2 days). Picking inclusive counting adds 1 day so both boundary dates count, while exclusive counting from Jan 1 to Dec 31, 2026 gives 364 days. To skip weekends on each step, use the business days calculator, or sum clock time in the time duration calculator.

Months do not share one length: they run 28, 29, 30, or 31 days. To split a span into years, months, and days, we step the start date forward by whole months without passing the end date. When a 31-day month steps into a shorter month, the day clamps to that month's last day. One month after Jan 31, 2026 is Feb 28, 2026, plus 2 more days to reach Mar 2, 2026 (30 days, or 1 month, 2 days). For birth dates and leap-year birthdays, open the age calculator.

Each full 7-day week holds 5 weekdays (Monday to Friday) and 2 weekend days (Saturday and Sunday). Any leftover days (d mod 7) are checked by their day of the week. Next, we check the federal holidays in 5 U.S.C. 6103(a): 11 of them since Juneteenth on June 19 was added by Pub. L. 117-17 on June 17, 2021, and 10 before that. Holidays are removed from 1986 on, the year the King birthday became a legal holiday; days before then count as ordinary weekdays. When a holiday falls on Saturday, the Friday before is observed under 5 U.S.C. 6103(b), and a Sunday holiday moves to Monday. Taking 6 weekday holidays out of the default span leaves 126 working days from Jan 1 to Jul 4, 2026.

Gregorian rata die, month-step, and weekday formulas

N(Y, M, D) = 146,097 × era + 365 × yoe + ⌊yoe ÷ 4⌋ − ⌊yoe ÷ 100⌋ + ⌊(153 × m + 2) ÷ 5⌋ + D − 719,469
d_excl = |N(Y₂, M₂, D₂) − N(Y₁, M₁, D₁)|; d_incl = d_excl + 1
Weeks = ⌊d ÷ 7⌋ weeks + (d mod 7) days
Net federal working days = Weekdays (Mon–Fri) − Observed 5 U.S.C. 6103 holidays on Mon–Fri

Worked date-difference examples

Default span (Jan 1, 2026 to Jul 4, 2026, exclusive): Jan 1, 2026 is day N₁ = 20,454 (Thursday). Jul 4, 2026 is day N₂ = 20,638 (Saturday). Subtracting gives 20,638 − 20,454 = 184 days, or 26 weeks, 2 days. Stepping 6 months from Jan 1, 2026 reaches Jul 1, 2026 plus 3 days (6 months, 3 days). Those 184 days split into 132 weekdays and 52 weekend days. Six federal holidays land on weekdays in that window: Jan 1, Jan 19, Feb 16, May 25, Jun 19, and Friday, Jul 3, 2026 (observed for Saturday, Jul 4).

Leap-year February vs 365-day February and 180-day offset: From Feb 1, 2024 to Mar 1, 2024, the year 2024 is divisible by 4, so Feb 29 adds 1 day. That span has 29 days (4 weeks, 1 day). It holds 21 weekdays, 1 holiday on Feb 19, and 20 working days. Over the same dates in 2026 (Feb 1 to Mar 1, 2026), there are 28 days (4 weeks, 0 days). That span has 20 weekdays and 19 working days. In offset mode, adding 180 days to Oct 1, 2026 (N = 20,727) gives N = 20,907. That date is 2027-03-30 (Tuesday) (25 weeks, 5 days, or 5 months, 29 days).

Assumptions, leap years, and 5 U.S.C. 6103 holidays

• Gregorian leap years (U.S. Naval Observatory). “Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400.” This adds 97 leap days every 400 years (146,097 days total, or 20,871 exact weeks) for a mean year of 365.2425 days.
• Whole calendar days and Daylight Saving Time (NIST). Most of the country observes Daylight Saving Time, but not Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands, or most of Arizona. Where it applies, clocks spring forward on the second Sunday of March (March 8, 2026, a 23-hour day). Clocks fall back on the first Sunday of November (November 1, 2026, a 25-hour day). Date subtraction counts whole calendar dates rather than local clock hours. Hour and second totals use the exact 24-hour SI day (1,440 minutes = 86,400 seconds) in NIST SP 811, Appendix B.8.
• Federal holidays (5 U.S.C. 6103 and OPM). Title 5, section 6103(a) names 11 annual holidays. The first five are New Year's Day (Jan 1), MLK Jr.'s Birthday (3rd Mon in Jan), Washington's Birthday (3rd Mon in Feb), Memorial Day (last Mon in May), and Juneteenth (Jun 19). The next six are Independence Day (Jul 4), Labor Day (1st Mon in Sep), Columbus Day (2nd Mon in Oct), Veterans Day (Nov 11), Thanksgiving (4th Thu in Nov), and Christmas (Dec 25). Under 5 U.S.C. 6103(b), a Saturday holiday is observed on the Friday before, such as Friday, Jul 3, 2026 and Friday, Dec 31, 2027. Under Executive Order 11582 section 3(a), a Sunday holiday is observed on the following Monday. Inauguration Day (January 20 of each fourth year after 1965) is a holiday under 5 U.S.C. 6103(c) only for employees in the Washington, D.C. area, so the net working days do not remove it. Holidays are removed from 1986 on, the year the King birthday became a legal holiday. Each year from 1986 uses the dates above, with Juneteenth only from 2021. Halloween (Oct 31) and Valentine's Day (Feb 14) are fixed dates, not 5 U.S.C. 6103 holidays.

What to do with your day and date count

Use exclusive counting for court periods and many interest statements. Exclusive counting gives 184 days from Jan 1 to Jul 4, 2026, the same count as Fed. R. Civ. P. 6(a)(1), which leaves out the start day and counts the last. Check whether your statement counts up to or through the payoff date. The daily interest calculator opens with the choice you made here and asks for its own dates.

Switch to inclusive counting when both dates count. A full year from Jan 1 to Dec 31, 2026 is 365 days inclusive. Dec 17 to Dec 31, 2026 is 15 days inclusive, the length of a taxable year that starts on Dec 17. The California LLC annual tax and fee calculator tests the 15-day test in Cal. Rev. & Tax. Code § 17946, which also requires that no business was done in California.

Check weekend and holiday shifts on your end date. Day 45 after Oct 1, 2026 lands on 2026-11-15 (Sunday). The offsets table shifts a date past weekends and District of Columbia holidays. The 1031 exchange deadline calculator and the stock trade settlement date calculator work out their own deadlines.

Separate working days from calendar days. In the default window, 132 weekdays and 52 weekend days minus 6 weekday holidays leave 126 working days. Use the business days calculator when a contract counts business days.

Questions about counting days between dates