Get calendar days between two dates

Question

The DateDiff function reports Day Intervals on a 24 hour basis, which provides an odd result when asking how many days ago something happened when the time of day changes.

For example, if I want to get the number of days since yesterday afternoon, if it hasn't been a full 24 hours, DateDiff will return 0, whereas most of the time I ask that question, I'm expecting yesterday to be treated as 1 day ago, regardless of timestamp.

Is there a way to get DateDiff to return the number of calendar days?

Demo in .NET Fiddle

Dim date1 As DateTime = #3/1/2017 5:00 PM#
Dim date2 As DateTime = #3/2/2017 10:00 AM#

Dim daysAgo = DateDiff(DateInterval.Day, date1, date2)
Dim msg = String.Format("Last date was {0} day(s) ago on {1}. ", daysAgo, date1.ToShortDateString())
Console.WriteLine(msg) ' Last date was 0 day(s) ago on 3/1/2017.

The following questions on StackOverflow do not address this nuance:

Why don't you subtract one date from the other? The resulting TimeSpan shows both full days and fractional days — Panagiotis Kanavos, Mar 02 '17 at 16:34
*Why* round? TimeSpan.Days returns the days as an integer. `(date2.Date-date1.Date).Days ` will get you the days — Panagiotis Kanavos, Mar 02 '17 at 16:47

score 10 · Accepted Answer · answered Mar 02 '17 at 16:44

You don't need string manipulation to get a DateTime without the time part, just use DateTime.Date.

To get the time span between two dates, just subtract one from the other. Subtracting one date from another returns a TimeSpan object whose Days property is the difference in full dates.

All you need to do is :

Dim days As Integer =(date2.Date-date1.Date).Days

This way you avoid generating and parsing temporary strings.

KyleMit · Answer 2 · 2017-03-02T18:28:58.640

0

You can use DateTime.Date to remove the time component and compare the whole number dates like this:

Demo in .NET Fiddle

Dim date1 As DateTime = #3/1/2017 5:00 PM#
Dim date2 As DateTime = #3/2/2017 10:00 AM#

Dim daysAgo = DateDiff(DateInterval.Day, date1.Date, date2.Date)
Dim msg = String.Format("Last date was {0} day(s) ago on {1}. ", daysAgo, date1.ToShortDateString())
Console.WriteLine(msg) ' Last date was 1 day(s) ago on 3/1/2017.

edited Mar 02 '17 at 18:28

answered Mar 02 '17 at 16:30

KyleMit

30,350
66
462
664

3

Or just use `DateTime.Date` and avoid the temporary strings – Panagiotis Kanavos Mar 02 '17 at 16:35

Get calendar days between two dates

Demo in .NET Fiddle

2 Answers2

Demo in .NET Fiddle