Mabye this is an easy one for you Airtable gurus. I am currently creating a more or less complex ToDo list and want to create a field which calculates the difference between Estimate and ACTUAL use of time. Does anyone know a simple trick or formula to solve this? Many thanks in advance !

# Calculate the difference in hours based on two time fields [SOLVED]

This is pretty simple, but you have to just keep in mind that a “Duration” field holds its value in seconds.

So if you have a duration field, and you enter `1:00`

in it to represent 1 hour, and then you create a formula field that just returns the value of that duration field, you’ll find that the formula field returns `3600`

- because there are 3600 seconds in an hour.

The implication is that if you have two duration fields (`Expected`

and `Actual`

), and you subtract one from the other in a formula field, you need to divide the result by 3600 if you want it to return in hours; or by 60 if you want it to return in minutes.

When `Expected`

= `1:00`

And `Actual`

= `1:02`

`Difference`

=

```
({Expected} - {Actual})/60 & " minutes"
```

will return `-2 minutes`

(Seeing the reply that was just sent in above mine, it becomes evident that you weren’t talking about duration fields… maybe someone will still find this useful anyhow )

**Alec_East**#5

Thank you very much. As I inserted the formula it seems that the time difference is not being viewed or summed up. Therefore, must I remove the minutes? What can i do that it detects it as a value? Many thanks in advance.

**Alec_East**#6

@Jacob_Turley As I inserted your formula, there was a failure. Is the “hours” part being inserted as well or is this value also changed/customized according to the table?

**Alec_East**#8

I am using a duration fields. According to that it sums them up, what the formula field unfortunately isn’t. Is there a solution to sum up these values when collapsed in group?

**Alec_East**#9

## The solution in calculating the difference and summing it up is the formula:

({Expected} - {Actual})/60

After adding the formula into the “Formula field” you simply have to group (by whatever value you like; Can be per month or day, or by task type) and then collapse the whole group.

After collapsing the group, click on “sum” and choose “sum” from the dropdown.