How the calculator adds time
Time does not add up like ordinary numbers, because 60 seconds make a minute and 60 minutes make an hour. The calculator turns every row into milliseconds, adds or subtracts them, and turns the total back into hours, minutes, seconds and milliseconds.
Here is the example that the calculator starts with:
- 1 hour 45 minutes 30 seconds is 6,330,000 milliseconds.
- 38 minutes 45.25 seconds is 2,325,250 milliseconds.
- Together they make 8,655,250 milliseconds, which is 2:24:15.250.
Adding time to a time of day
The second card answers questions like “what time is it 2 hours and 45 minutes after 9:30 AM?” The answer is 12:15 PM.
When the result goes past midnight, the calculator marks it +1 day. Subtracting can reach back into the day before, which is marked −1 day. A shift that starts at 10:00 PM and lasts 9 hours ends at 7:00 AM, +1 day.
Time between two times
The third card counts the time from one clock time to another. If the second time is earlier than the first, the calculator assumes it is on the next day, so 10:15 PM to 6:40 AM is 8 hours 25 minutes.
The result is also shown as decimal hours, which is handy for timesheets. 8 hours 25 minutes is 8.42 hours.
Converting between units
To turn minutes into hours, divide by 60. To turn hours into minutes, multiply by 60. The same goes for seconds and minutes. A few common conversions:
- 1 hour is 60 minutes, 3,600 seconds or 3,600,000 milliseconds.
- 90 minutes is 1.5 hours.
- 2.25 hours is 2 hours 15 minutes.
- 0.75 hours is 45 minutes.
- 1 day is 24 hours, 1,440 minutes or 86,400 seconds.
Questions and answers
How do I add hours and minutes together?
Add the minutes first. For every 60 minutes, carry one hour over. For example, 2:40 plus 1:35 is 3 hours and 75 minutes, which is 4 hours 15 minutes. The calculator does the carrying for you.
How do I subtract time?
Switch a row to minus and it is taken away from the total. If you take away more than you have, the result is shown as a negative time, such as −0:15:00.
Can I add milliseconds?
Yes. Each row has a milliseconds field, and the total shows three digits after the seconds, such as 2:24:15.250. This is useful for lap times and video editing.
How do I convert minutes to hours?
Divide the minutes by 60. 135 minutes divided by 60 is 2.25 hours, which is 2 hours 15 minutes. The totals under the result show the same time in hours, minutes, seconds and milliseconds.
What time will it be in 8 hours?
Use the second card. Enter the current time as the start, keep it on plus and type 8 in the hours field. If the result is after midnight, it shows +1 day.
How do I work out hours worked overnight?
Use the third card. Enter the start and end of the shift. When the end is earlier than the start, the calculator counts it as the next morning, so 10:00 PM to 6:30 AM is 8 hours 30 minutes, or 8.5 hours.