Time Calculator

DateMath adds the days, hours, minutes and seconds to the start as one amount, so values above 24 hours or 60 minutes roll over and a result past midnight moves to the right date, month and year. Times are clock times without a time zone, so adding 24 hours always gives the same clock time on the next day.

• The Gregorian calendar. DateMath treats every date as a Gregorian date, with its leap-year rule: a year divisible by 4 is a leap year, except century years not divisible by 400, so 2000 had a February 29 and 2100 will not. Source: Gregorian calendar.

DateMath's date math is tested against more than 100 cases worked out by hand. Every worked example and table on the site is computed with the same code the calculators run, so a page and its calculator can't disagree.

The time calculator adds days, hours, minutes and seconds to a date and time, or subtracts them, and gives the exact date, weekday and clock time that results. Because the start includes a date, it works as a time and date calculator: a result past midnight moves to the next day, and one past the end of a month or year lands in the right month and year, with leap days included.

What you enter

• Start date and time, to the minute, in your browser's date and time picker.
• Add (+) or Subtract (−): forward to find what time it will be, backward to find what time it was.
• Days, Hours, Minutes and Seconds: whole numbers of 0 or more, with no limit per field. Values over 60 or 24 roll over, so you can type 90 minutes or 100 hours as they are.

What you get

The headline gives the weekday, date and 12-hour time, such as Friday, March 5, 2027, 5:30 PM. The Date and time line below gives the same moment in 24-hour form, 2027-03-05 17:30. Results can fall anywhere in the years 1 to 9999, and the copy-link button saves the calculation.

The calculator works from one date and time and an amount. If you need a time and date calculator between two dates, the hours and minutes from one date and time to another, use the date duration calculator. To add calendar months or years, whose length varies, use the date calculator.

Add the hours to the current time; past 12:00 AM (midnight) the day moves on. Subtract them to go back. In the calculator, press Now next to the start to set it to your current date and time, choose Add or Subtract and type the hours. Whole days of hours keep the clock time: 24 hours, 48 hours and 72 hours from now are the same time 1, 2 and 3 days later. This table starts at Monday, March 8, 2027, 9:00 AM:

Adding minutes

Type minutes into the Minutes field as they are; there is no need to convert them to hours first. Starting at 11:30 PM Friday, close to midnight, most results fall on the next day:

Write both times in 24-hour form, so you don't have to track AM and PM, and add from the smallest unit up. Every full 60 seconds carries 1 minute, every 60 minutes 1 hour and every 24 hours 1 day. Example: Friday, March 5, 2027, 9:47:35 PM (21:47:35) plus 5 hours, 38 minutes, 50 seconds.

1. Seconds: 35 + 50 = 85, which is 1 minute and 25 seconds. Write 25, carry 1.
2. Minutes: 47 + 38 + 1 carried = 86, which is 1 hour and 26 minutes. Write 26, carry 1.
3. Hours: 21 + 5 + 1 carried = 27, which is 1 day and 3 hours. Write 3, carry 1.
4. Date: move 1 day forward, from Friday, March 5, 2027 to Saturday, March 6, 2027.

Result: Saturday, March 6, 2027, 3:26:25 AM (03:26:25), the same as the calculator gives.

Subtract from the smallest unit up. When a unit is too small, borrow 1 from the next one: an hour gives 60 minutes, a day 24 hours. Example: Monday, March 1, 2027, 2:15 AM (02:15) minus 4 hours, 40 minutes, which crosses both midnight and a month end.

1. Minutes: 15 is less than 40, so borrow 1 hour (60 minutes): 15 + 60 = 75, and 75 − 40 = 35.
2. Hours: 2 − 1 borrowed = 1. 1 is less than 4, so borrow 1 day (24 hours): 1 + 24 = 25, and 25 − 4 = 21.
3. Date: go back 1 day, from Monday, March 1, 2027 to Sunday, February 28, 2027.

Result: Sunday, February 28, 2027, 9:35 PM (21:35). When the date goes back past the 1st, the day before is the last day of the previous month, which for February depends on the leap year; the calculator handles that for you.

DateMath works in clock time without a time zone, so it never skips or repeats an hour. Adding 24 hours always gives the same clock time the next day: Saturday, March 13, 2027, 12:00 PM plus 24 hours is Sunday, March 14, 2027, 12:00 PM. In most of the United States the clocks spring forward at 2:00 AM on Sunday, March 14, 2027, so between those two times only 23 hours actually pass.

For elapsed hours across the change, such as a night shift, correct the result by that hour yourself: 10:00 PM Saturday plus 8 hours gives 6:00 AM Sunday here, but after 8 real hours a clock that sprang forward reads 7:00 AM. On the fall-back night (Sunday, November 7, 2027) it reads 5:00 AM instead of 6:00 AM. Time zones are not applied either: for a flight, the result is in the departure's time zone.

The 12-hour clock, common in the United States, uses AM from midnight until just before noon and PM from noon until just before midnight. The 24-hour clock numbers the hours 00:00 to 23:00. The calculator shows both: 12-hour time in the headline and 24-hour time in the Date and time line.

• Midnight is 12:00 AM, or 00:00. It starts a day, so 1 hour after 11:00 PM Friday is 12:00 AM Saturday.
• Noon is 12:00 PM, or 12:00.
• From 12-hour to 24-hour: add 12 to PM hours from 1 to 11, so 3:30 PM is 15:30. From 24-hour to 12-hour: subtract 12 from hours 13 to 23 and write PM.
• There is no 24:00 in the calculator: the end of a day is 00:00 on the next day.

Timesheets and payroll often record hours as decimals. To turn minutes into decimal hours, divide them by 60. To turn decimal hours back into minutes, multiply the part after the point by 60: 7.75 hours is 7 hours, 45 minutes, because 0.75 × 60 = 45. Don't read a decimal as hours and minutes: 7.3 hours is 7 hours, 18 minutes, not 7 hours 30 minutes.

The calculator takes whole numbers, so convert decimal hours before you enter them: 7.75 hours goes in as 7 hours, 45 minutes, or as 465 minutes in the Minutes field.

Totaling a timesheet

Add the hours and the minutes separately, then carry every 60 minutes into an hour. For 5 shifts of 7:45, 8:20, 6:50, 8:05 and 7:30 (hours:minutes), the hours add up to 36 and the minutes to 150, which is 2 hours, 30 minutes. The total is 38 hours, 30 minutes, or 38.5 decimal hours. For the hours between a clock-in and a clock-out time, use the hours calculator; to total a week of shifts with breaks, the time card calculator; and to convert any amount, the hours to decimal calculator.

The calculator uses fixed units: a minute is 60 seconds, an hour 60 minutes, a day 24 hours and a week 7 days. A large amount in one field is the same as its rolled-over parts, so you can enter whichever is easier:

• Shift end times. A shift from 7:00 AM lasting 8 hours 30 minutes ends at 3:30 PM; a 12-hour night shift from 10:00 PM Monday ends at 10:00 AM Tuesday.
• Deadlines in hours. A 72-hour window that opens Friday, March 5, 2027, 3:00 PM closes Monday, March 8, 2027, 3:00 PM. For deadlines in working days, use the business days calculator.
• Arrival times. A 7 hour 25 minute flight leaving at 6:40 PM Friday lands at 2:05 AM Saturday departure time; add or subtract the time zone difference yourself.
• Long counts. 1,000 hours from Monday, January 4, 2027, 9:00 AM is Monday, February 15, 2027, 1:00 AM.

For a date a number of weeks, months or years away, use the date calculator; to see which week a result falls in, the week number calculator; for an exact age, the age calculator.