Date maths, durations and epochs

Duration between dates

Enter a start and end date to measure the gap between them. From 1 September to 8 September is seven days; the same date at both ends is zero. Reversing the dates makes the total negative. Hours and minutes are the day count multiplied by 24 and 1,440, not actual elapsed clock time through daylight-saving changes.

Add or subtract from a date

Apply years, then months, then weeks and days to the start date. Calendar overflow carries into the next month: adding one month to 31 January 2026 gives 3 March, rather than the last day of February. Check the result when starting near a month end.

Business days

Count Monday through Friday, including both endpoints when they are weekdays. Monday 7 September through Friday 11 September 2026 gives five business days. Public holidays are not removed, even if a holiday falls within that range. The working-hours figure assumes eight hours per counted weekday.

Week number and day facts

Look up the ISO week and week year, day of year and leap-year status for one date. ISO weeks begin on Monday; early January can belong to the previous week year. For example, 1 January 2021 is in week 53 of 2020.

Birthday countdown

Enter a date of birth to see age, days lived and the next birthday. The input stays in this page and is not uploaded. A 29 February birthday is treated as 1 March in a non-leap year. Birthstones, flowers and zodiac labels are cultural associations, not predictions or health information.

Unix epoch converter

Convert a timestamp into UTC and local time, or convert a device-local date and time into seconds and milliseconds. Timestamp 0 is 1 January 1970 at 00:00 UTC. Inputs with an absolute value above 100,000,000,000 are interpreted as milliseconds; smaller values are seconds. This heuristic suits modern timestamps but can misread millisecond values close to 1970. The two inputs are independent; editing one does not overwrite the other.

A gap of a week

From 1 September 2026 to 8 September 2026 the duration calculator gives seven total days, a calendar breakdown of 0y 0m 7d, 1.0 weeks, 168 hours and 10,080 minutes. Put the later date in the From field instead and the day, hour and minute figures all turn negative, while the breakdown and the week count are reported as magnitudes and stay positive.

Seventeen days ahead

Starting from 18 September 2026 and adding 2 weeks and 3 days lands on Monday 5 October 2026, ISO week 41 of 2026, day 278 of the year. Weeks are converted to seven days each and applied with the days, after the years and months have been added, so the four boxes are not independent steps you can reorder.

A month of working days

From 1 to 30 September 2026 the business day calculator counts 22 business days, 8 weekend days, 30 days in total and 176 working hours at eight per weekday. A public holiday inside that range is counted as an ordinary working day, so subtract those yourself before quoting the figure as capacity.

A round timestamp

Typing 1000000000 into the epoch converter resolves to 9 September 2001 at 01:46:40 UTC, with the local line showing the same instant in this device's zone. The local line and the UTC line will fall on different calendar dates for anyone far enough east or west, which is the usual reason a timestamp appears to disagree with a log file.

Five of the six calculators work on calendar dates with no time of day attached, which is why a clock change never shifts an answer by an hour and why the hour and minute figures are conversions of a day count rather than measured elapsed time. The epoch converter is the exception: it deals in instants, and its two fields are the same instant written two ways.

The exact age in the birthday tool is counted forward from the birth date, so the leftover day figure depends on the length of the month you are currently in. Days lived is a plain count of calendar days and does not have that wobble. The star sign, birthstone and flower use the common fixed date boundaries; other traditions place some of those boundaries a day either side, so treat a birthday that falls on a cusp as a label rather than a fact.

In the week number panel, the quarter is calendar based rather than fiscal, and the days remaining figure counts the days after the one you entered, so 31 December returns zero rather than one. Leap year refers to the year of the date you typed, which matters when you are checking whether a February deadline has a 29th in it.