Date & Time Calculators

Why a dedicated date calculator beats mental math

The Gregorian calendar is irregular by design. Months run 28, 29, 30 or 31 days; February gains a day in years divisible by four, except century years that are not divisible by 400, which is why 2000 was a leap year and 1900 was not. Counting across those boundaries by hand invites off-by-one slips, and spreadsheet date functions vary in how they treat the end date. These tools count whole calendar days using exact integer arithmetic and state clearly whether the end date is included.

No time-zone or daylight-saving surprises

Many web date tools quietly measure the gap between two midnights in milliseconds and divide by the length of a day. When a daylight-saving change falls inside the range, one of those "days" is 23 or 25 hours long and the result can come out a day short. Our calculators never look at clock time. Each date is converted to a day number on the proleptic Gregorian calendar — the same count of days since 1 January 1970 that UTC timestamps use — and the answer is a simple subtraction or addition of whole numbers. The result is the same wherever you are and whatever time of year it is.

What each tool does

• Days Between Dates counts calendar days, weeks plus leftover days, the year-month-day span, and how many of those days fall on weekdays versus weekends — useful for notice periods, project timelines and countdowns.
• Age Calculator gives an exact age in years, months and days on any date, the total months, weeks and days lived, the weekday of birth and a countdown to the next birthday, with a clear rule for 29 February birthdays.
• Add or Subtract Days moves a date by days, weeks, months or years. Month and year steps keep the same day number where it exists and otherwise land on the last day of the month, so 31 January plus one month gives the end of February.
• Countdown to a Date shows the calendar days left until an event, the weekdays and weekend days remaining, and a live clock ticking down to the second.
• Time Card Calculator totals hours worked from start and end times, subtracts unpaid breaks, handles overnight shifts and can split weekly overtime and estimate gross pay.
• Time Duration Calculator finds the hours and minutes between two clock times, past midnight or across several dates, in clock and decimal formats.

Supported range and input format

Dates from year 1 to year 9999 are accepted in the ISO format YYYY-MM-DD, which is what the date pickers in modern browsers produce. Dates before the Gregorian reform of 1582 are calculated on the proleptic calendar — the modern rules extended backwards — which matches how most software and astronomers handle historical dates but not necessarily the calendar people used at the time. For genealogical research involving older Julian-calendar records, convert the dates first.

Weekends, holidays and business days

The days-between tool separates Monday-to-Friday days from Saturdays and Sundays. It does not remove public holidays, because they vary by country, region and employer. If your deadline counts only working days, subtract your local holidays from the weekday figure. For contracts and legal deadlines, always check the counting rule written into the agreement, since some count the first day and others do not.