Time Calculator

Add or Subtract Duration from Time

Calculating Time Math

Calculating time is distinct from normal decimal math because it uses a "sexagesimal" system (base-60) for minutes and seconds, and a base-24 system for hours. You cannot simply add 1.50 + 1.50 to get 3 hours; in time notation, 1 hour 50 minutes plus 1 hour 50 minutes equals 3 hours 40 minutes.

Common Use Cases

  • Work Hours: Calculating total hours worked by adding a shift duration to a start time.
  • Flight Arrival: Adding flight duration to a departure time (often involving crossing midnight).
  • Video Editing: Summing up the lengths of multiple video clips to find total runtime.
  • Event Planning: Working backwards from a deadline by subtracting prep time.
[Image of time math clock face]

24-Hour vs. 12-Hour Format

This calculator uses the 24-hour format (00:00 to 23:59) to ensure precision and avoid AM/PM ambiguity during calculation.

  • 00:00 is Midnight.
  • 12:00 is Noon.
  • 18:00 is 6:00 PM.

Step-by-Step Instructions

  1. Enter Start Time: Input the initial time in Hours, Minutes, and Seconds.
  2. Select Operator: Choose "+" to add time (find a future time) or "-" to subtract time (find a past time).
  3. Enter Duration: Input the amount of time you want to add or subtract. You can include Days (DD), Hours (HH), Minutes (MM), and Seconds (SS).
  4. View Result: The calculator displays the final result instantly.