Time Calculator

Add, subtract, and calculate time in days, hours, minutes, and seconds. Includes time expression parser and date offset calculator.

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How Time Arithmetic Works

Time uses a mixed-radix system: 60 seconds per minute, 60 minutes per hour, and 24 hours per day. Adding and subtracting requires carrying and borrowing across these boundaries, unlike base-10 math.

Three Calculators

Add / Subtract Time: Combine two time durations. Enter days, hours, minutes, seconds for each and choose add or subtract.
Time from Date: Start with a specific date and time, then add or subtract a duration to get the resulting date. Useful for deadline calculations and scheduling.
Time Expression: Type a freeform expression like 1d 2h 3m + 4h 5s - 2030s and get the evaluated result.

Common Units of Time

Like other numbers, time can be added or subtracted. However, due to how time is defined, there are differences in how calculations must be computed when compared to decimal numbers. The following table shows some common units of time.

Unit	Definition
millennium	1,000 years
century	100 years
decade	10 years
year (average)	365.242 days or 12 months
common year	365 days or 12 months
leap year	366 days or 12 months
quarter	3 months
month	28–31 days Jan., Mar., May, Jul., Aug., Oct., Dec.—31 days Apr., Jun., Sep., Nov.—30 days Feb.—28 days for a common year and 29 days for a leap year
week	7 days
day	24 hours or 1,440 minutes or 86,400 seconds
hour	60 minutes or 3,600 seconds
minute	60 seconds
second	base unit
millisecond	10⁻³ second
microsecond	10⁻⁶ second
nanosecond	10⁻⁹ second
picosecond	10⁻¹² second

Practical Uses

Project planning: Add estimated task durations to find total project time
Travel: Calculate arrival time by adding flight duration to departure time across time zones
Cooking: Sum multiple prep and cook times for meal planning
Exercise: Track total workout duration across multiple sets and rest periods
Work hours: Add up daily time entries for weekly or monthly totals

Time Expression Syntax

The expression parser accepts values with unit suffixes:

d — days
h — hours
m — minutes
s — seconds

Use + and − between terms. Example: 2d 5h + 3h 30m - 45m 20s

Related Calculators

Age Calculator: Your Exact Age in Years, Months, Days Calculate your exact age in years, months, and days from your date of birth. See age in weeks, hours, and total days, plus a reference table of common ages in every unit. How Old Was I Calculator — Age on Any Past Date Find out how old you were on any date. Calculate age in years, months, days, hours, minutes, and seconds. Add Times Calculator — Sum HH:MM:SS Durations Add multiple time durations together in hours, minutes, and seconds. Get results in HH:MM:SS and decimal hours. Time Until Calculator — Live Countdown to Any Date Calculate the time remaining until a specific time and date. Live countdown in days, hours, minutes, and seconds. How Many Days Until School Ends? Live Countdown Live countdown to the end of the school year showing remaining school days (weekdays) and calendar days in real time, plus a weeks-to-school-days reference and dismissal-time mode. Weeks Between Dates Calculator — Plus Days & Months Calculate the number of weeks between two dates. Also shows total days, months, weekdays, and weekend days.

Frequently Asked Questions

How many seconds are in a day?

There are 86,400 seconds in a day: 24 hours × 60 minutes × 60 seconds. A week holds 604,800 seconds. An hour is 3,600 seconds and a minute is 60, so any duration converts to seconds by multiplying the hours by 3,600 and the minutes by 60, then adding the parts together.

How many minutes are in a day?

There are 1,440 minutes in a day (24 × 60). A week contains 10,080 minutes and a standard 30-day month contains 43,200 minutes. To turn minutes back into hours, divide by 60: 1,440 minutes is 24 hours, and 90 minutes is 1.5 hours, or 1 hour 30 minutes.

What is 2 hours 45 minutes plus 1 hour 30 minutes?

2 hours 45 minutes plus 1 hour 30 minutes equals 4 hours 15 minutes. Add the hours (3) and the minutes (75) separately, then carry every 60 minutes into an extra hour: 75 minutes is 1 hour 15 minutes, giving 4 hours 15 minutes. The same carry rule turns 60 seconds into a minute and 24 hours into a day.

How do you subtract time in hours and minutes?

Subtract minutes from minutes and hours from hours, borrowing 60 minutes from the hours when the minutes would go negative. For 5 hours 10 minutes minus 2 hours 45 minutes, borrow to make 4 hours 70 minutes, then subtract to get 2 hours 25 minutes. Taking a larger time from a smaller one gives a negative result: 1h minus 2h 30m is -1h 30m.