Time Calculator
Add or subtract hours, minutes, and seconds from any time. Convert times to decimal hours, calculate durations, and handle midnight crossings automatically.
RESULT
12:15:00
09:30:00 + 2h 45m 0s = 12h 15m 0s
💡 How the Time Calculator Works
This calculator performs arithmetic on time values. Enter a starting time in 24-hour format, choose to add or subtract, then enter the hours, minutes, and seconds to adjust by. The result automatically wraps around midnight — if you add 5 hours to 10:00 PM, you get 3:00 AM.
Common uses include calculating end times for meetings, cooking timers, flight arrivals across time zones, and shift scheduling. The tool handles all the tricky edge cases like crossing midnight and minute/second overflow automatically.
Time arithmetic is something we all need but rarely enjoy doing manually. Whether you're scheduling meetings across US time zones, planning cooking times, calculating shift differentials, or figuring out when your flight lands, a time calculator eliminates the mental gymnastics of carrying over minutes and hours.
How to Add Times
Adding two times (or a time and a duration) follows a simple carry-over process:
- Add the seconds together. If the result is 60 or more, subtract 60 from the seconds and carry 1 to the minutes.
- Add the minutes together (plus any carry). If the result is 60 or more, subtract 60 from the minutes and carry 1 to the hours.
- Add the hours together (plus any carry). If the result is 24 or more, subtract 24 (the time wraps past midnight into the next day).
Example: 10:45:30 PM + 3h 25m 40s
- Seconds: 30 + 40 = 70 → 10 seconds, carry 1
- Minutes: 45 + 25 + 1 = 71 → 11 minutes, carry 1
- Hours: 22 + 3 + 1 = 26 → 26 − 24 = 2:11:10 AM (next day)
How to Subtract Times
Subtracting times works in reverse with borrowing:
- Subtract the seconds. If the result is negative, add 60 to the seconds and borrow 1 from the minutes.
- Subtract the minutes. If the result is negative, add 60 to the minutes and borrow 1 from the hours.
- Subtract the hours. If the result is negative, add 24 (the time wraps backward past midnight).
Example: 2:15:00 AM − 4h 30m = 22:15 − 0:30 → 9:45:00 PM (previous day)
Converting Time to Decimal
Many payroll systems, billing software, and scheduling tools require time in decimal format rather than hours:minutes. Here are the three conversion formulas:
| Convert To | Formula | Example (2h 30m 45s) |
|---|---|---|
| Decimal Hours | H + (M ÷ 60) + (S ÷ 3,600) | 2 + 0.5 + 0.0125 = 2.5125 hours |
| Decimal Minutes | (H × 60) + M + (S ÷ 60) | 120 + 30 + 0.75 = 150.75 minutes |
| Total Seconds | (H × 3,600) + (M × 60) + S | 7,200 + 1,800 + 45 = 9,045 seconds |
Common Time Conversions
| Minutes | Decimal Hours | Common Use |
|---|---|---|
| 6 min | 0.10 hrs | Billing in 6-min increments (legal) |
| 15 min | 0.25 hrs | Quarter-hour payroll rounding |
| 30 min | 0.50 hrs | Half-hour scheduling blocks |
| 45 min | 0.75 hrs | Class periods, therapy sessions |
| 90 min | 1.50 hrs | Movie length, meetings |
| 480 min | 8.00 hrs | Standard US work day |
Calculating Time Duration
To find the duration between two times:
- Convert both times to 24-hour format. 3:00 PM = 15:00. 8:30 AM = 08:30.
- Convert to decimal hours. 15:00 = 15.0 hours. 08:30 = 8.5 hours.
- Subtract. 15.0 − 8.5 = 6.5 hours = 6h 30m
If the end time is before the start time (overnight span), add 24 to the end time first. Example: 10:00 PM to 6:00 AM = (6 + 24) − 22 = 8 hours.
US Time Zones Quick Reference
| Zone | Abbreviation | UTC Offset (Standard) | UTC Offset (DST) |
|---|---|---|---|
| Eastern | EST / EDT | UTC−5 | UTC−4 |
| Central | CST / CDT | UTC−6 | UTC−5 |
| Mountain | MST / MDT | UTC−7 | UTC−6 |
| Pacific | PST / PDT | UTC−8 | UTC−7 |
| Alaska | AKST / AKDT | UTC−9 | UTC−8 |
| Hawaii | HST | UTC−10 | No DST |
Daylight saving time (DST) runs from the second Sunday in March to the first Sunday in November. Arizona (except Navajo Nation) and Hawaii do not observe DST.