Skip to content
DailyCalc

Date & Time Calculators

Ages, durations and working days

Age Calculator Exact age in years, months and days — plus zodiac, birthstone and next birthday. Date Difference Calculator The span between two dates in years, months, days, weeks and hours. Add or Subtract Days Calculator Find the date a given number of days, weeks, months or years away. Working Days Calculator Business days between two dates, excluding weekends and holidays. Time Duration Calculator Add up hours and minutes, or find the gap between two clock times. Unix Timestamp Converter Converts epoch time to a readable date and back, detecting seconds, milliseconds or microseconds. Time to Decimal Converter Turns hours and minutes into decimal hours for payroll, and back again. Military Time Converter Converts between the 24-hour clock and 12-hour AM/PM, including the midnight and noon traps. Timesheet Calculator Adds up a week of shifts with breaks, in hours and minutes and in decimal hours. Time Zone Converter Converts a time between any two zones, following daylight saving on the date you pick.

Why date arithmetic is harder than it looks

Dates do not behave like numbers. Months have different lengths, years occasionally have an extra day, and clocks jump forward and back twice a year in most of the world. Adding one month to 31 January has no unambiguous answer, and every library resolves it by convention rather than by logic. The tools here use the calendar rules explicitly and say which convention they follow, rather than producing a figure whose meaning you have to guess.

The age and date difference calculators return years, months and days rather than only a day count, because that is how the answer is normally wanted — and getting there requires walking the calendar rather than dividing by 365.25. Working days goes further and removes weekends and holidays, which is what a contractual deadline or a shipping estimate actually depends on.

Clock time, payroll and machine time

The time tools serve a different need: turning durations into something a payroll system or a spreadsheet can use. The time duration calculator adds up hours and minutes or finds the gap between two clock times across midnight. The timesheet calculator does a full week of shifts with breaks. Time to decimal converts 7 hours 45 minutes into 7.75, which is the form nearly every payroll system expects and the source of a great many quiet rounding errors.

Unix timestamps and the 24-hour clock are the machine-facing end. The timestamp converter detects automatically whether a number is in seconds, milliseconds or microseconds, since the difference is three orders of magnitude and easy to get wrong. The military time converter handles the two cases that trip people up every time: 12 AM is 0000 and 12 PM is 1200, not the other way round.

The time zone converter follows daylight saving as it stood on the date you pick, rather than as it stands today — which is what makes it usable for scheduling something months ahead.

Date & Time calculators — common questions

How is exact age calculated?

By walking the calendar rather than dividing. The calculator takes the whole years between the two dates, then the whole months remaining, then the days — so someone born on 29 February gets an age that increments on the date their birthday falls in a common year, and no answer relies on an average year length.

Do the working days calculators know about holidays?

They exclude weekends automatically and let you add specific holiday dates yourself. Public holidays vary by country, by region and sometimes by employer, so building in a fixed list would give a confidently wrong answer for most users rather than an obviously incomplete one.

Why does adding a month sometimes not change the day of the month?

Because the target month may not have that day. Adding one month to 31 January has to land somewhere, and the convention used here clamps to the last valid day — 28 or 29 February — rather than overflowing into March. The date add and subtract calculator states this on its own page, since the alternative convention is equally defensible and gives a different answer.

Do these tools handle daylight saving time?

The time zone converter does, applying the rules in force on the date you select rather than today’s offset. The duration and timesheet calculators work in plain clock time and do not adjust for a DST transition inside the period, which matters only on the two days a year when a shift spans the change.