Time Calculator
Add or subtract hours & minutes
Time Operations
About Time Calculation
Time is unique because it doesn't follow the standard decimal system (Base-10). Instead, it uses a mix of Base-12 (Hours), Base-60 (Minutes/Seconds), and Base-24 (Days). This makes mental math extremely difficult. This calculator handles the complex conversions instantly, perfect for payroll, flight planning, or just figuring out when your shift ends.
How to Use This Calculator
Step-by-Step
- 1Select the operation: 'Add Time' (e.g., What time will it be in 8 hours?) or 'Subtract Time' (e.g., What time was it 3 hours ago?).
- 2Enter the Starting Time. You can use AM/PM or 24-hour format.
- 3Enter the Duration you want to add or subtract (Hours and Minutes).
- 4The result updates instantly.
Pro Tips
- ✓Use 24-hour format (Military Time) whenever possible to completely avoid AM/PM ambiguity.
- ✓If you need to calculate 'Hours Worked' (Start Time vs End Time), used the 'Duration' mode if available, or simply find the difference.
- ✓Remember that 00:00 is midnight and 12:00 is noon.
The Math Behind It
Why is calculating time so hard? It's because of the Sexagesimal system (Base-60), which dates back to ancient Sumeria.
The Modulo Operation
To add minutes, we use the modulo operator (remainder).
Example: 2:50 PM + 20 minutes.
50 + 20 = 70 minutes.
70 / 60 = 1 hour with a remainder of 10 minutes.
So we add 1 hour to the clock and set minutes to 10.
Result: 3:10 PM.
The Midnight Crossing
When you cross midnight (24:00 or 00:00), the date changes.
Example: 11:00 PM + 2 hours.
23:00 + 2 hours = 25:00.
25 - 24 = 1:00.
Result: 1:00 AM (Next Day).
Real World Applications
Payroll & Time Cards
Employees often write "9:00 to 5:15". To calculate pay, you need the total hours. This is 8 hours and 15 minutes. For payroll, you convert 15 minutes to decimals: 15/60 = 0.25. Total Pay Hours = 8.25.
Flight Planning
If a flight departs New York at 3:00 PM EST and is 6 hours long, when does it land in London (which is +5 hours ahead)?
3:00 PM + 6 hours = 9:00 PM (NYC Time).
9:00 PM + 5 hours (Zone Change) = 2:00 AM (London Time).
Cooking & Baking
" Roast the turkey for 4 hours and 30 minutes. Let it rest for 20 minutes." If you start at 11:00 AM, you add 4h 30m = 3:30 PM. Add 20m rest = 3:50 PM serving time.
Frequently Asked Questions
How do I calculate the time between two times?
To calculate the duration between two times, subtract the start time from the end time. If the timeframe crosses midnight, add 24 hours to the end time before subtracting. For example, 10 PM (22:00) to 2 AM (02:00 + 24 = 26:00) is 4 hours.
How do I add hours to a time?
To add hours, simply add the number of hours to the current hour. If the result is greater than 12 (for 12-hour format) or 24 (for 24-hour format), subtract 12 or 24 respectively and adjust AM/PM or the date accordingly.
What is military time?
Military time (or 24-hour clock) counts hours from 00:00 (midnight) to 23:59. It eliminates confusion between AM and PM. For example, 1:00 PM is 13:00, and 5:30 PM is 17:30.
How do I convert minutes to decimal hours for payroll?
Divide the minutes by 60. For example, 30 minutes = 30/60 = 0.5 hours. 15 minutes = 15/60 = 0.25 hours. So 8 hours and 15 minutes is 8.25 hours.
Does this calculator handle leap years?
For simple time addition (hours/minutes), leap years don't apply. However, our Date Calculator (separate tool) does account for leap years when calculating days between dates.