Elapsed time means the amount of time that passes between a start time and an end time. To find it, count on from the start: first to the next whole hour, then in whole hours, then the leftover minutes. Example: from 8:40 to 11:15 is 20 minutes (to 9:00) + 2 hours (to 11:00) + 15 minutes = 2 hours 35 minutes.
Reviewed by the Helping with Math Team · Updated 14 October 2026
What does elapsed time mean?
Elapsed time is how much time has gone by from the start of an event to its end. If a movie starts at 2:00 p.m. and ends at 3:45 p.m., the elapsed time is 1 hour 45 minutes. You need two of these three facts to find the third: the start time, the end time and the elapsed time.
We measure time with clocks and calendars, in seconds, minutes, hours, days, weeks, months and years. This page covers reading clocks, a.m. and p.m., the 24-hour clock, and the number line method for elapsed time, with a calculator to check answers.
Hours, minutes and seconds
Time is measured in hours, minutes and seconds. How are these three related to each other?
1 minute = 60 seconds
1 hour = 60 minutes
This means that 1 hour = 60 × 60 = 3,600 seconds
A second is a very short period of time, say the time that is taken to blink your eye, to snap your fingers etc. It is a smaller unit of time than a minute.
Reading a clock to the exact minute
To understand how to tell time to exact minute, let us consider an example.
Suppose Victor and his sister Alice were going to school. When they started from home, the following time was shown by the clock:
Victor asked her to read the time. She read it easily as 7:30. Then they reached the school and the time shown by the clock in the school is
Victor again asked her to read the time. But, she was not able to read the time to the exact minutes. Now, Victor told her it was 8:10. Let us understand how to read time to exact minutes.
If you see carefully, there are 12 numbers and 60 divisions on the face of a clock. Therefore, we have,
1 hour = 60 minutes.
Hence, the number of divisions between two consecutive numbers is 60 ÷ 12 = 5 divisions or 5 minutes.
We will read the time on the given clock as 2:07 if,
- The hour hand of the clock is at 2
- The minute hand of the clock is at the 2nd division after the 1st number, 7 minutes (1 × 5 = 5, plus 2 more minutes = 7 minutes).
Hence, we can say that the numbers on the clock actually represent hours and the divisions between them represent the minutes.
It is important to know here that:
Quarter of an hour = 60 ÷ 4 = 15 minutes
Half of an hour = 60 ÷ 2 = 30 minutes.
12:00 o’clock in the night is 12:00 midnight
12:00 o’clock at the daytime is 12:00 noon
12:00 noon is 12 p.m. and 12:00 midnight is 12 a.m. Writing “noon” or “midnight” avoids mix-ups.
How long does each hand take to go once around the clock?
- The hour hand of the clock goes round the clock in 12 hours.
- The minute hand completes one round in 1 hour.
- The second hand completes one round in 1 minute
Time in a.m. and p.m.
We can observe that there are 12 numbers written on the face of a clock. We also know that a day has 24 hours. Therefore, the hour hand of the clock completes 1 round in 12 hours. So, we divide 24 hours of a day in two periods:
- From 12:00 midnight to 12:00 noon
- From 12:00 noon to 12:00 midnight
The time between 12:00 midnight to 12:00 noon is written as a.m. Here a.m. means ante meridiem which means before midday.
The time between 12:00 noon and 12:00 midnight is known as p.m. Here p.m. means post meridiem which means after midday.
Another thing that should be noticed is that at times we see time written in a.m. or p.m. while at times it is written as, say, 16:00 with no mention of a.m. and p.m.
12-hour clock vs 24-hour clock
There are two ways of telling the time:
The 12-hour clock runs from 1am to 12 noon and then from 1pm to 12 midnight.
The 24-hour clock uses the numbers 00:00 to 23:59 (midnight is 00:00).
Let us do a time comparison between the two styles of telling time.
| 12-hour Clock | 24-hour Clock |
| 1:00 am | 1:00 |
| 2:00 am | 2:00 |
| 3:00 am | 3:00 |
| 4:00 am | 4:00 |
| 5:00 am | 5:00 |
| 6:00 am | 6:00 |
| 7:00 am | 7:00 |
| 8:00 am | 8:00 |
| 9:00 am | 9:00 |
| 10:00 am | 10:00 |
| 11:00 am | 11:00 |
| 12:00 noon | 12:00 |
| 1:00 pm | 13:00 |
| 2:00 pm | 14:00 |
| 3:00 pm | 15:00 |
| 4:00 pm | 16:00 |
| 5:00 pm | 17:00 |
| 6:00 pm | 18:00 |
| 7:00 pm | 19:00 |
| 8:00 pm | 20:00 |
| 9:00 pm | 21:00 |
| 10:00 pm | 22:00 |
| 11:00 pm | 23:00 |
| 12:00 midnight | 00:00 (start of the next day) |
Analog and digital clocks
We see different types of clocks everywhere around us. What is a clock? A clock is an instrument to measure time which is shown in hours, minutes and seconds. There are two types of clocks −
Analog Clock:Analog clocks use hands to show the hours, minutes and seconds. There are two hands in the analog clocks:
The little hand shows the hour.
The bigger hand shows the minutes.
In many clocks, there is another big constantly moving hand that shows the seconds.
Digital Clock:Digital clocks use numbers to show the hours and minutes such as 5:35.
Consider the clock shown above. We can see that there is a short hand at 5 which represents the hour, while the bigger hand at 3 represents the minutes. So, the time is 5:15, or a quarter past 5.
Third Hand of a Clock
Many of the clocks have three hands instead of two. What is this third hand for? The third hand is usually long and thin, and it is called the second hand. The seconds hand takes 60 seconds to complete one round of the clock.
Therefore, 1 minute = 60 seconds.
Hence the second hand is a smaller unit of time than a minute.
Thus, second is the smallest unit and hour is the largest unit among the three units of time i.e. hour, minute and second.
When the second hand moves once around the clock the minute hand moves through 1 minute
Finding elapsed time on a number line
Since time is not represented using a decimal system, the difference in time between 2:05 and 1:55 is 0:10 as opposed to 0:50. In other words, conventional subtraction suggesting that 2:05 − 1:55 = 0:50 is incorrect. A good alternative to subtraction (which will still work sometimes e.g. 2:30 − 2:15) is to use an “add-on” method. This is best done using or visualizing a number line. A number line is an excellent tool when working with elapsed time. Below is a representation of elapsed time on a number line:
From 8:40 a.m. to 11:15 a.m.: 20 min + 2 hours + 15 min = 2 hours 35 minutes.
Let us consider an example. What would be the elapsed time between 8:40 and 9:00? We now know that it would be 20 minutes between 8:40 and 9:00. Similarly, what would be the elapsed time between 9:00 and 11:00. It would be 2 hours. How can we represent these on a number line? Below is the representation of these on a number line:
Using Number Line to represent elapsed one hour
Each jump of one hour moves the time on by 1 hour. Two one-hour jumps take 2:00 to 4:00 −
Using Number Line to represent elapsed 2 hours or more
What if we wish to show a jump of 2 hours or 3 hours? Below is the representation of the same on the number line:
Using points on a number line as stepping stones to understand elapsed time
We can use the points on a number line as “ stepping stones ” and add on smaller “chunks of time” to find the total elapsed time. Below is an example, showing an elapsed time of 2 hours and 30 minutes:
Another way to add-on with the number line is to take as many 1 hour steps as we can before going past the end time. In the example below, from 3:15 to 5:30, the first step is from 3:15 to 4:15. The second step is from 4:15 to 5:15. Another one hour step would take us too far along the line so we stop after 2 hour steps and then find what needs to be added on to get to the end time. Here we need a 15 minute final step to give a total elapsed time of 2 hours 15 minutes.
Elapsed time across 12 o’clock
The hours go 9, 10, 11, 12, 1, 2, so counting past 12 is where most mistakes happen. The time number line helps as we can use 12 as a “stepping stone” and break the elapsed time into manageable “chunks of time.” Below we have an example, showing elapsed time between 8:30 and 2:15 −
It is important to remember here that there are no rules to these methods. We can identify and use whatever “chunks of time” are easiest for us. For instance, we can represent the elapsed time between 7:45 and 10:21 as follows:
Elapsed time examples
Example 1
Dinner will be ready in 45 minutes. It is 6:30 p.m. now. What time will dinner be ready?
Solution
Start at 6:30 p.m. and count on. 30 minutes takes you to the next hour, 7:00 p.m. That leaves 45 − 30 = 15 minutes, and 15 minutes after 7:00 p.m. is 7:15 p.m. Dinner will be ready at 7:15 p.m.
Example 2
Change these 24-hour clock times to 12-hour clock times: a) 11:15 b) 16:40
Solution
a) 11 is less than 12, so the time is in the morning: 11:15 is 11:15 a.m. b) 16 is more than 12, so subtract 12: 16 − 12 = 4, and 16:40 is 4:40 p.m.
Example 3
Alicia’s flight from Atlanta to New York leaves at 9:15 a.m. and takes 2 hours 15 minutes. What time does it land?
Solution
Jump the whole hours first: 9:15 a.m. plus 1 hour is 10:15 a.m., plus another hour is 11:15 a.m. Then add the 15 minutes: 11:30 a.m. The plane lands at 11:30 a.m. (Atlanta and New York are in the same time zone.)
Example 4
A soccer practice runs from 8:30 a.m. to 2:15 p.m. How long is it?
Solution
8:30 to 9:00 is 30 minutes. 9:00 to 2:00 is 5 hours (use 12:00 noon as a stepping stone: 3 hours to noon, then 2 more). 2:00 to 2:15 is 15 minutes. Total: 5 hours 45 minutes.
Key facts and summary
- Elapsed time is the time that passes between a start time and an end time.
- 1 minute = 60 seconds and 1 hour = 60 minutes, so 1 hour = 3,600 seconds.
- Count on with a number line: to the next whole hour, then whole hours, then leftover minutes.
- Do not subtract times like decimals: 2:05 − 1:55 is 10 minutes, not 50.
- A quarter of an hour is 15 minutes; half an hour is 30 minutes.
- a.m. is from midnight to noon; p.m. is from noon to midnight.
- 24-hour times after 12:59 are p.m.: subtract 12 to get the 12-hour time (16:40 is 4:40 p.m.).
More practice: elapsed time worksheets, estimating and rounding time worksheets and world time zones worksheets.
Elapsed time FAQs
What does elapsed time mean?
The amount of time that passes from a start time to an end time. A class from 9:00 to 9:50 has an elapsed time of 50 minutes.
How do you calculate elapsed time?
Count on from the start time: minutes to the next whole hour, then whole hours, then the leftover minutes. Add the jumps. From 1:45 to 4:15: 15 min + 2 h + 15 min = 2 h 30 min.
Why can’t I just subtract the times?
Because an hour has 60 minutes, not 100. 2:05 − 1:55 looks like 0:50, but the real gap is 10 minutes. Counting on avoids this.
How do I find elapsed time across noon or midnight?
Use 12:00 as a stepping stone. From 8:30 a.m. to 2:15 p.m.: 30 min to 9:00, 3 h to noon, 2 h to 2:00, 15 min to 2:15. Total 5 h 45 min.
How do I find the end time?
Add the elapsed time to the start time, hours first, then minutes. 9:15 a.m. plus 2 h 15 min is 11:30 a.m.
What time is 16:00?
16:00 on the 24-hour clock is 4:00 p.m. Subtract 12 from any hour from 13 to 23 to get the p.m. time.
