Calculating with Time
Even otherwise highly numerate people have been known to throw up their hands in horror at the thought of adding together times.
A system like time, which is not decimal, can be counterintuitive and requires concentration.
However, with a bit of application, you too can learn how to calculate with time, and gain confidence in manipulating hours, minutes and seconds.
A system like time, which is not decimal, can be counterintuitive and requires concentration.
However, with a bit of application, you too can learn how to calculate with time, and gain confidence in manipulating hours, minutes and seconds.
Basic Units of Time
The basic units of time, which allow you to do calculations involving time, are:
Years are commonly split into quarters, especially in business and education settings with each quarter being three months or approximately 90 days. Quarters in a specific business or sector may not necessarily be the same as those indicated below:
The number of days in a month varies. All months have the same number of days each year except for February which has 28 days in a common year and 29 in a leap year.
The number of days in a month varies. All months have the same number of days each year except for February which has 28 days in a common year and 29 in a leap year.
As the number of days in a month varies this also means that the number of weeks in a month varies too.
People often use approximations when calculating the number of days in months. For example, it is common to use the assumption that a month contains four weeks, even though only February in a common year actually does so.
This makes it hard to convert from months to weeks and vice versa, unless you know which months are being used, because there is no immediate ‘conversion factor’.
People often use approximations when calculating the number of days in months. For example, it is common to use the assumption that a month contains four weeks, even though only February in a common year actually does so.
This makes it hard to convert from months to weeks and vice versa, unless you know which months are being used, because there is no immediate ‘conversion factor’.
Writing Time
There are many different ways to write time. The simplest (digital) form is as written hh.mm or hh:mm, for example 10.21 or 10:21.
Hours may be either divided into 24 or two lots of 12, in which case all those before noon are designated am (ante meridiem) and those after noon are pm (post meridiem). For example 4:10pm is the same time as 16:10.
You can also describe time in words, such as 'ten minutes past/after twelve', or 'ten past twelve'. Up to half way through an hour, we describe ‘minutes past’ the hour; beyond ‘half past’ we talk about minutes to/before the next hour.
Hours may be either divided into 24 or two lots of 12, in which case all those before noon are designated am (ante meridiem) and those after noon are pm (post meridiem). For example 4:10pm is the same time as 16:10.
You can also describe time in words, such as 'ten minutes past/after twelve', or 'ten past twelve'. Up to half way through an hour, we describe ‘minutes past’ the hour; beyond ‘half past’ we talk about minutes to/before the next hour.
Example time formats:
Calculating the Passage of Time
In the normal way of things, to calculate how much one thing is greater than another you would simply subtract one from another. However, subtracting time is complicated because it’s not decimal. Instead of the columns being hundreds, tens and units, they are hours, minutes and seconds.
The other way of calculating how much time has passed between Time A and Time B is:
 Work out how many minutes from Time A to the next hour (or minute, if in minutes and seconds).
 Work out how many hours between that next hour, and the last whole hour before Time B.
 Work out how many minutes from the whole hour until time B.
 Add these three numbers together.
Worked Examples
Pat was due to catch a train at 11.44am, which she has just missed. The next train is not until 1.17pm. How long will she have to wait? Before you start, convert all the numbers to 24hour clock for ease. 11.44am becomes 1144 and 1.17pm becomes 1317.
I am organising a series of canoe races, and have synchronised clocks for the start and the finish. The plan is for the first race to start at about 30 minutes after synchronisation, then four more races to start at 2minute intervals after that, but it never works exactly. The starter keeps a record of the exact times, and it turns out that on this occasion, races started at 28:02, 30:00, 32:15, 34:40 and 37:00.
The finish line has a clock, which is exactly synchronised with the start clock, and the finisher records the time on the clock when the racers cross the finish line. For each of the following finish times, work out how long the competitor took (click on the + icons to see the working and answers):

Conclusion
The most important thing when calculating with time is to check whether the answer looks about right?
If your two numbers are less than an hour apart, is your answer less than an hour? If they are about 2 hours apart when you look at them, is your answer? If not, you may have lost or gained some time somewhere!
Read more at: https://www.skillsyouneed.com/num/calculatingtime.html
If your two numbers are less than an hour apart, is your answer less than an hour? If they are about 2 hours apart when you look at them, is your answer? If not, you may have lost or gained some time somewhere!
Read more at: https://www.skillsyouneed.com/num/calculatingtime.html
Add Hours Minutes Seconds to Time CalculationOn the following time calculation steps,
we show how to add time in seconds. Let's say starting time is 2:15:30 Add 4:50:15 1 hour = 60 × 60 seconds 1 minute = 60 seconds Calculating starting time in seconds 2:15:30 = (2×60×60 sec) + (15×60 sec) + 30 sec = (7200 sec) + (900 sec) + 30 sec = 8130 seconds To add 4:50:15 to starting time We calculate seconds too 4:50:15 = (4×60×60 sec) + (50×60 sec) + 15 sec = (14400 sec) + (3000 sec) + 15 sec = 17415 seconds Now let's add starting seconds = 8130 seconds + 17415 seconds = 25545 seconds Calculating days 1 day = 24 hours 1 day = 24×60×60 seconds 1 day = 86400 seconds We got 25545 seconds total days = 25545 ÷ 86400 total days = 0 Calculating hours We got 25545 seconds total hours = 25545 sec ÷ (60×60 sec) total hours = 7 hours We have left 25545 seconds  (7×60×60) sec = 25545  25200 sec = 345 seconds Calculating minutes total minutes = 345 ÷ 60 total minutes = 5 minutes We have left = 345  (5 × 60) seconds = 45 seconds So the result is 2:15:30 + 4:50:15  7:05:45 
Subtract Hours Minutes Seconds from Time CalculationOn the following time calculation steps,
we show how to subtract time in seconds. Let's say starting time is 2:15:30 Subtract 0:50:15 1 hour = 60 × 60 seconds 1 minute = 60 seconds Calculating starting time in seconds 2:15:30 = (2×60×60 sec) + (15×60 sec) + 30 sec = (7200 sec) + (900 sec) + 30 sec = 8130 seconds To subtract 0:50:15 from starting time We calculate seconds too 0:50:15 = (50×60 sec) + 15 sec = (3000 sec) + 15 sec = 3015 seconds Now let's subtract from starting seconds = 8130 seconds  3015 seconds = 5115 seconds Calculating days 1 day = 24 hours 1 day = 24×60×60 seconds 1 day = 86400 seconds We got 5115 seconds total days = 5115 ÷ 86400 total days = 0 Calculating hours We got 5115 seconds total hours = 5115 sec ÷ (60×60 sec) total hours = 1 hour We have left 5115 seconds  (1×60×60) sec = 5115  3600 sec = 1515 seconds Calculating minutes total minutes = 1515 ÷ 60 total minutes = 25 minutes We have left = 1515  (25 × 60) seconds = 15 seconds So the result is 2:15:30  0:50:15  1:25:15 
ABOUT TIME TO DECIMAL CONVERTER
Enter the time values in HH:MM:SS
How to Calculate Decimal from Time
How to Calculate Decimal from Time
 To get the total decimal hours we use the formula: h = hours + (minutes / 60) + (seconds / 3600).
 To get the total decimal minutes we use the formula: m = (hours * 60) + minutes + (seconds / 60).
 To get the total decimal seconds we use the formula: s = (hours * 3600) + (minutes * 60) + seconds.
 Note that; 1 hour is equal to 60 minutes or 3600 seconds.