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 - 2030sand 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