We've had some trouble with the DateDiff function when calculating the number of days remaining. It looks like there is a bug.
It appears to take fractional parts of the days and if there is more than half a day remainder, round up the result, which looks like there is an extra day.
DateDiff(DateTimeValue("02/03/2020 11:00 PM"),DateTimeValue("02/07/2020 10:00 PM"),Days) should equal 3 but returns 4
Looking at the hours, then dividing by 24
DateDiff(DateTimeValue("02/03/2020 11:00 PM"),DateTimeValue("02/07/2020 10:00 PM"),Hours) / 24
returns 3.9~ which then gets upped to 4, which explains why the bug is occurring.
We worked around this bug by using a round down,
RoundDown(DateDiff(timeNow, expiryDate, Hours) / 24,0)
but it took a lot of investigation time. It appears someone has already raised a similar defect with DateDiff around Years back in 2018 but it doesn't look like it was addressed.
To track down the bug we built a datatable in powerapps and compared different ways of calculating the date. You can see for the dates with a fractional difference above 3.5, things get rounded up for DateDiff days (see the 2nd row and 4th last row)
Whats the best way to lodge this as a bug? I think having correctness shouldn't be a feature request
Thanks for your feedback.
I will submit this issue to PowerApps Team and hope it will be fixed in the next Update. If there is any update, I will post back.
Also discovered that calculations based on hours suffered the same issue (eg if there were greater than 2h 30m remaining), datediff hours would round up and show 3h remaining
@v-siky-msft any update on this issue?
I just noticed someone replying to a ideas post from 2018 about it
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