Date Calculator
Compare many dates or calculate many offsets from one base date.
Results
Date counting rules shown with every row
The base date is day 0 by default. A target on the following date is 1 calendar day after it, and a date in the past is labeled before rather than relying on a minus sign alone. Include both dates adds the two endpoints to an interval. This is useful only when the rule you are following explicitly uses inclusive counting.
Calculations use date-only Gregorian calendar values, so a daylight-saving clock change cannot add or remove a day. Calendar-month and calendar-year shifts clamp to the last valid day of the destination month: January 31 plus one month becomes February 28 in 2026, while February 29 plus one year becomes February 28.
Compare a milestone list two ways
Base date mode compares every valid row with one common start. Previous milestone mode turns the same list into a timeline: the first row starts at the base date, and each later row starts at the previous valid milestone. Sort dates first when a pasted list is out of order. Use unambiguous YYYY-MM-DD dates or explicit U.S. MM/DD/YYYY dates; invalid rows stay visible by line number and do not break the remaining calculations.
The summary reports the full earliest-to-latest span, the longest displayed gap, and the average displayed gap. Copy table produces tab-separated columns that paste cleanly into spreadsheets without uploading the dates.
Add or subtract several offsets from one date
Use a leading plus or minus sign to make the direction explicit, such as Review | +14 or Cutoff | -30. One line still works as a normal date calculation; several lines create a reusable deadline table without repeating the base date.
Working days and custom closures
Monday through Friday is the default, but it is not universal. Open Workdays and holidays to choose the days that count and paste any dates that should not count. The calculator excludes the start, counts toward the end, removes duplicate holiday entries, and never subtracts a holiday twice when it already falls on a non-working day.
No location-specific public holidays are built in. That keeps the result honest for company shutdowns and non-U.S. workweeks, but it also means the output is only as complete as the dates you enter.
Frequently asked questions
How do I calculate days between two dates?
Choose the first date as the base date, then enter the other date on its own line. The default result excludes the base date and counts the target date, so the next calendar date is 1 day after. Turn on Include both dates when your rule counts both endpoints.
Can I compare several dates at once?
Yes. Paste up to 50 dates, one per line. You can add labels with the format Launch | 2026-12-25. Compare every row to the base date or build a timeline in which each row is compared with the previous valid milestone.
Can I add or subtract days from one date?
Yes. Open Add or subtract and enter signed offsets such as +7, +30, or -14. Each line produces a separate result. You can use calendar days, working days, weeks, calendar months, or calendar years.
Does this date calculator exclude holidays?
Only dates you enter under Workdays and holidays are excluded. No federal, state, company, school, or religious holiday calendar is assumed. A holiday that already falls on a non-working day is not deducted twice.
Are business days the same everywhere?
No. The default working week is Monday through Friday, but you can select any working days. The page calls them working days because local holidays and workplace rules vary.
Can I use the result for a legal deadline?
Use it as planning arithmetic, not legal advice. Court, tax, contract, and filing rules may define holidays, cutoff times, service dates, or inclusive counting differently. Confirm those rules with the relevant authority.