Add or Subtract the hours and minutes separately.
But you may need to do some adjusting if the minutes end up 60 or more, or less than zero!

• If the minutes are 60 or more, subtract 60 from the minutes and add 1 to hours

Like this:

### Easy example: What is 2:45 + 1:10 ?

Add the Hours: 2+1 = 3
Add the Minutes: 45+10 = 55

The minutes are OK, so the answer is 3:55

### Hard example: What is 2:45 + 1:20 ?

Add the Hours: 2+1 = 3
Add the Minutes: 45+20 = 65

The minutes are 60 or more, so

• subtract 60 from minutes (65−60 = 5 Minutes)
• and add 1 to Hours (3+1 = 4 Hours)

## Subtracting Times

• Subtract the hours
• Subtract the minutes
• If the minutes are negative, add 60 to the minutes and subtract 1 from hours.

Like this:

### Easy example: What is 4:10 - 1:05 ?

Subtract the Hours: 4−1 = 3
Subtract the Minutes: 10−5 = 5

The minutes are OK, so the answer is 3:05

### Hard example: What is 4:10 - 1:35 ?

Subtract the Hours: 4−1 = 3
Subtract the Minutes: 10−35 = −25

The minutes are less than 0, so:

• add 60 to Minutes (−25+60 = 60−25 = 35 Minutes)
• and subtract 1 from Hours (3−1 = 2 Hours)

(Note: did you see how we changed "−25+60" to "60−25" ... that is perfectly fine and makes the calculation easier.)

The hours can also end up too large or small!

To fix that first we must know if it is 24-Hour Clock or AM/PM: ### 24-Hour Clock

• When Hours end up less than zero: add 24
• When hours end up more than 23: subtract 24

### Example: What is 16:20 + 9:35 ?

Add the Hours: 16+9 = 25
Add the Minutes: 20+35 = 55

The minutes are OK

The hours are more than 23, so subtract 24: 25−24 = 1

The answer is 1:55 of the next day.

### Example: What is 4:10 − 6:15 ?

Subtract the Hours: 4−6 = −2
Subtract the Minutes: 10−15 = −5

The minutes are less than 0, so:

• add 60 to Minutes: −5+60 = 60−5 = 55 Minutes
• and subtract 1 from Hours: −2−1 = −3 Hours

The hours are less than 0, so add 24: −3+24 = 24−3 = 21

The answer is 21:55 of the previous day.

### 12-Hour Clock (AM/PM)

For 12-Hour Clock it is best to convert to 24-Hour Clock, do the calculations then convert back.

### Example: What is 3:20 PM − 16:05 ?

3:20 PM is 15:20

Subtract the Hours: 15−16 = −1
Subtract the Minutes: 20−5 = 15

The minutes are OK

The hours are less than 1, so add 24: −1+24 = 24−1 = 23

The answer is 23:15, which is 11:15 PM of the previous day.