# Calculate the number of days between two datetimes?

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Jussi Ikäheimo on 10 Nov 2016
Commented: Peter Perkins on 18 Nov 2016
How to calculate the number of days between two datetimes?
days(between(day1,day2)) does not work:
"Error using days (line xxx) Input data must be a real, numeric array."

Brendan Hamm on 10 Nov 2016
You can do:
days(day2-day1)
The issue is that the between function returns a calendarDuration and this is measured using variable time-frames like months and years which contain different numbers of days.

### More Answers (1)

Peter Perkins on 15 Nov 2016
between already calculated the difference between those two dates in days:
>> d1 = datetime('yesterday'); d2 = datetime('tomorrow');
>> between(d1,d2)
ans =
calendarDuration
2d
Even more explicitly:
> between(d1,d2,'days')
ans =
calendarDuration
2d
If you then want the number 2, use caldays:
>> caldays(between(d1,d2,'days'))
ans =
2
Hope this helps.
##### 2 CommentsShow NoneHide None
Jussi Ikäheimo on 17 Nov 2016
It seems that the 'days' option is needed in between(), otherwise an error results.
Peter Perkins on 18 Nov 2016
Jussi, I'm not sure what you're saying. All I wanted to demonstrate was that between gives you back a quantity that already measures the number of days. If you need a numeric value, then caldays is the function you want to apply to that, not days.