Date Calculator
Date math made easy: add or subtract time from a date, find the difference between two dates, count business days, and inspect a date (weekday, ISO week, day of year, quarter, days remaining).
About this tool
This date calculator does four common date jobs in one place. Add or subtract a span (years, months, weeks, days, hours, minutes, seconds) from a starting date — calendar math for months/years (so adding one month to Jan 31 lands on Feb 28/29), linear math for the smaller units. Difference breaks two dates into total days, hours, minutes, seconds, and a calendar-style "1y 2m 15d" breakdown. Business days counts working days between two dates, letting you pick a custom weekend (Mon–Fri, Sun–Thu, anything) and exclude a list of holidays. Date info inspects a single date: weekday, ISO week, day of year, quarter, leap year, days remaining in the month and year, and the Unix timestamp.
Example: add 45 days to 2026-01-01 → 2026-02-15. Business days from 2026-01-01 to 2026-01-31 (Mon–Fri, no holidays) → 21.
FAQ
Does adding months roll over the day? ›
Adding one month to January 31 gives February 28 (or 29 in a leap year), because the target day is clamped to the length of the destination month. Adding one month to January 15 gives February 15 as expected.
How are business days counted? ›
The tool walks every calendar day in the range and counts those that fall on a selected working day and are not in your holiday list. Weekends and holidays are reported separately. Dates are always compared in ascending order regardless of which order you enter them.
Which week numbering system does Date info use? ›
ISO 8601 weeks (Monday is the first day, and the week with the first Thursday is week 1). This is why the ISO week number can differ from a naive count near the start or end of the year.
Does this account for time zones or daylight saving? ›
Calculations use the local time zone of your browser. The difference mode works with date-times, so a DST transition can shift the hour totals by one hour; use the days breakdown for unambiguous durations.
How is this different from the Age Calculator? ›
The Date Calculator handles generic date math — add or subtract time from any date, find the difference between any two dates, count business days, and inspect calendar properties like ISO week, quarter, and day of year. For age-specific calculations from a birth date (exact age in years/months/days, days until next birthday, total heartbeats), use the dedicated <a href="/age-calculator">Age Calculator</a>.