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elapsed time — Definition, Formula & Examples

Elapsed time is the amount of time that passes from a start time to an end time. For example, if you begin reading at 2:00 PM and stop at 2:45 PM, the elapsed time is 45 minutes.

Elapsed time is the measured duration between two specific points in time, calculated as the difference between the end time and the start time, expressed in appropriate units such as minutes, hours, or a combination of both.

Key Formula

Elapsed Time=End Time−Start Time\text{Elapsed Time} = \text{End Time} - \text{Start Time}
Where:
  • End Time\text{End Time} = The time at which an event finishes
  • Start Time\text{Start Time} = The time at which an event begins

How It Works

To find elapsed time, count forward from the start time to the end time. One helpful strategy is to count to the next full hour first, then count the remaining minutes. If the start time is 9:40 AM and the end time is 11:15 AM, you can count 20 minutes to reach 10:00 AM, then 1 hour to reach 11:00 AM, and finally 15 more minutes to reach 11:15 AM. Add those pieces together: 20 min + 1 hr + 15 min = 1 hour 35 minutes. A number line or an open timeline drawn on paper can make this counting easier to see.

Worked Example

Problem: A movie starts at 4:25 PM and ends at 6:10 PM. How much time has elapsed?
Count to the next hour: From 4:25 PM to 5:00 PM is 35 minutes.
5:00−4:25=35 min5{:}00 - 4{:}25 = 35 \text{ min}
Count whole hours: From 5:00 PM to 6:00 PM is 1 hour.
6:00−5:00=1 hr6{:}00 - 5{:}00 = 1 \text{ hr}
Count remaining minutes: From 6:00 PM to 6:10 PM is 10 minutes.
6:10−6:00=10 min6{:}10 - 6{:}00 = 10 \text{ min}
Add the parts: Combine all the pieces to get the total elapsed time.
35 min+1 hr+10 min=1 hr 45 min35 \text{ min} + 1 \text{ hr} + 10 \text{ min} = 1 \text{ hr } 45 \text{ min}
Answer: The elapsed time is 1 hour and 45 minutes.

Why It Matters

Figuring out elapsed time comes up constantly in daily life — planning how long a trip will take, knowing when a class ends, or tracking how long you practiced an instrument. In 3rd and 4th grade math (including NY Next Generation standards), elapsed time problems prepare you for working with intervals, schedules, and eventually rate problems in later grades.

Common Mistakes

Mistake: Subtracting minutes and hours as if time works like regular base-10 numbers (e.g., treating 3:50 to 5:10 as 5:10 − 3:50 = 2:60 hours).
Correction: Remember that each hour has only 60 minutes, not 100. Count forward in chunks — to the next hour, then by whole hours, then by remaining minutes — to avoid base-10 errors.

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