# Time Calculator – Add & Subtract Hours, Minutes, Seconds

There are different ways to measure the difference between two times. Like when you want to know the time difference between 8:00am and 6:45pm, you’ll get the answer 10.75 hours or 10 hours and 45 minutes.

But to arrive at that, you can either use a time calculator to make it convenient for you, or opt to do the math manually.

There are often many uses to  calculating the time difference from computing work hours for salaries, in time cards or for payrolls

## Time calculator

Now, when you want to add or subtract time, you can easily do so using this calculator. You may use our calculator to determine the span of future events by using + operator to add times, or you can calculate the time span between two points in time by subtracting them.

## To use the calculator

To use this online time calculator, simply key in a start time — provided with days, hours, minutes and even seconds. Choose the operation that you want to perform, whether addition or subtraction.

Then, key in the end time. You will also have the option to enter the time from the number of days, hours, minutes and even seconds.

Next, the calculator will automatically generate the time difference between the two time schedules you’ve entered. The results will be available in days, hours, minutes and also seconds.

## Compute time difference manually

For those opting to the math, here are the steps to compute the time difference manually:

1. Use the 24-hour format to make it easier to compute. That means adding 12 to all pm hours if necessary.
2. Subtract all end times from hours to minutes. If the start minutes is higher than the end minutes, subtract an hour from the end time hours and add 60 minutes to the end minutes.
3. Proceed to subtract the start time minutes to the end minutes.
4. Subtract the hours too from end to start.
5. Combine the hours and minutes results together to arrive at the answer.

## Tips to calculate easily

The easiest way to tell the time difference between two times is to use the online calculator. It is faster and more convenient. By inputting the start time and end time you can also compute the results with up to the last minutes and seconds in one click.

But for those that want to do manual computation, it is important to make sure that your times follows the same format.

## Common units of time

Time like other numbers can be added or subtracted. There’s also common units of time that everyone is familiar with which is used to refer to a particular set of time.

Unit of TimeWhat it means
millenium1,000 years
century100 years
year365.242 days or 12 months
leap year366 days or 12 months
quarter3 months
month28-31 days depending on the month
week7 days
day24 hours or 1,440 minutes
or 86,400 seconds
hour60 minutes or 3,600 seconds
minute60 seconds
secondbase unit of time

## Did you know?

• One of the earliest proponents of the concept of time is Greek philosopher Aristotle, who defined time back then as a “number of movements in respect of the before and after.”
• One of the most notable theories about time is Albert Einstein’s “Theory of Relativity” which states that “laws of physics are the same for all non-accelerating observers.” He said the speed of light within a vacuum is the same no matter the speed at which an observer travels.
• The Egyptians are often credited for being the first civilization on earth to divide the day into smaller units of time due to their use of sundials.
• The most widely-used calendar is the Gregorian calendar.
• The first pendulum mechanical clock was made by Christiaan Huygens, a Dutch physicist, in 1656.