Date & Time calculators
Date and time tools calculate exact ages, the days between dates, business days, countdowns, the day of the week for any date, ISO week numbers, time durations, hours worked, shift schedules, time zone conversions and Unix timestamps. They account for leap years, varying month lengths and daylight saving time so you do not have to.
15 tools · Updated October 21, 2026
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Why calendar arithmetic is tricky
Months have 28 to 31 days, and leap years add a day in February. In the Gregorian calendar, a year is a leap year if it is divisible by 4, except century years, which must be divisible by 400; so 2000 was a leap year and 1900 was not. Adding 'one month' to January 31 has no single right answer, which is why the Date Difference and Age calculators report results in more than one form.
Counting conventions matter too. Some contexts count both the start and end dates (inclusive), others count only the days between. The Business Days Calculator excludes weekends and lets you account for holidays, which vary by country and employer.
Durations, work hours and shifts
Time is base 60, so you cannot add 1.45 hours and 2.30 hours as decimals and expect the right answer. Convert to minutes, or use the Time Duration Calculator, which adds and subtracts hours, minutes and seconds correctly. Payroll often needs decimal hours (7 hours 45 minutes is 7.75 hours), which the Work Hours Calculator provides along with unpaid breaks.
Overnight shifts cross midnight, so an end time that looks earlier than the start time actually belongs to the next day. The Shift Schedule Creator builds a weekly roster from shift types (including an overnight shift), staff days off and preferences.
Time zones, daylight saving and Unix time
Time zones are offsets from Coordinated Universal Time (UTC), but those offsets change when regions enter or leave daylight saving time, and not on the same dates everywhere. The Time Zone Converter uses current zone rules, which is safer than adding a fixed number of hours.
Unix time counts seconds since 00:00:00 UTC on January 1, 1970, ignoring leap seconds. It is the standard way computers store moments in time. Some systems use milliseconds instead of seconds, so a 13-digit timestamp is usually milliseconds; the Unix Timestamp Converter detects both.