Dart/Flutter DateTime difference inDays error for March 31 April 1

Question

I am trying to get the difference in Days between two dates picked from a DatePicker. This works fine except for ONE single date : March 31.

The difference in Days between two DateTimes is wrong by 1 day when one of the dates is March 31. I know this is due to Light Saving and March is 30.9… days long and not 31, hence I am guessing, the error. But does anyone know how to fix this other than manually checking if a date is equal to March 31 and adding one day to the result ?

Two very simple examples that can be run in the Dart Pad :

DateTime aprilFirst = DateTime(2019, 3, 30);
DateTime marchThirtyFirst = DateTime(2019, 3, 31);

print(aprilFirst.difference(marchThirtyFirst).inDays); => -1

DateTime marchThirty = DateTime(2019, 4, 1);
DateTime marchThirtyFirst = DateTime(2019, 3, 31);

print(marchThirty.difference(marchThirtyFirst).inDays); => 0

UPDATE:

DateTime aprilFirst = DateTime(2019, 4, 1);
print(aprilFirst.add(Duration(days: -1))); => 2019-03-30 23:00:00.000

This should print 2019-03-31 23:00:00.000 !

I tried Günter Zöchbauer's solution of making the DateTimes UTC but the results are the exact same:

DateTime aprilFirst = DateTime(2019, 4, 1).toUtc();
DateTime marchThirty = DateTime(2019, 3, 30).toUtc();
DateTime marchThirtyFirst = DateTime(2019, 3, 31).toUtc();

print(aprilFirst.difference(marchThirtyFirst).inHours); => 23
print(aprilFirst.difference(marchThirtyFirst).inDays); => 0
print(marchThirty.difference(marchThirtyFirst).inHours); => -24
print(aprilFirst.add(Duration(days: -1))); => 019-03-30 22:00:00.000Z

@pskink There are 23 hours between March 31 and April 1. 24 hours for all the other dates. — Benjamin, Apr 02 '19 at 11:03

Benjamin · Accepted Answer · 2019-04-02T11:26:05.120

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@Günter Zöchbauer put me on the right path. DateTime(...).toUTC() will fail for difference calculations. However, using the DateTime.utc(...) constructor does the trick !

DateTime aprilFirst = DateTime.utc(2019, 4, 1);
DateTime marchThirty = DateTime.utc(2019, 3, 30);
DateTime marchThirtyFirst = DateTime.utc(2019, 3, 31);

print(aprilFirst.difference(marchThirtyFirst).inHours); => 24
print(aprilFirst.difference(marchThirtyFirst).inDays); => 1
print(marchThirty.difference(marchThirtyFirst).inHours); => -24
print(aprilFirst.add(Duration(days: -1))); => 2019-03-31 00:00:00.000Z

edited Apr 02 '19 at 11:26

answered Apr 02 '19 at 11:12

Benjamin

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I'll be so happy when we finally eliminate DST worldwide. It's just rediculous. – Randal Schwartz Apr 04 '19 at 19:25
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I know this is against protocol, but omg, I wasted one whole day trying to find out how this date time and daylight saving work. May the gods of bits and bytes bless you @Benjamin! – adrianvintu Mar 30 '20 at 20:42
This is still a rather strange behavior. One day out of all don't work?! – Schultz9999 Mar 31 '20 at 22:51
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@adrianvintu Did you waste a day or did you waste 23 hours? – Rem-D Aug 08 '20 at 13:44
@Rem-D hahaha, nice 1 :D – adrianvintu Aug 09 '20 at 14:15
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```DateTime.utc``` litteraly saved me hours of headache – M.M.Hasibuzzaman Feb 01 '22 at 17:37
Hi there I'm having a similar problem on my question and can't figure it out https://stackoverflow.com/questions/71589896/flutter-timer-resets-when-switching-pages-with-bottom-navigation-bar – LearnFlutter Mar 24 '22 at 08:34

score 4 · Answer 2 · answered Apr 02 '19 at 11:00

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Don't do Date comparison or operations with local dates. Convert it to UTC first. Otherwise daylight savings and other local DateTime related exceptions will cause all kinds of surprising effects.

DateTime aprilFirst = DateTime(2019, 3, 30).toUtc();
DateTime marchThirtyFirst = DateTime(2019, 3, 31).toUtc();

print(aprilFirst.difference(marchThirtyFirst).inDays); => -1

If the result is a DateTime you can convert it back using xxx.toLocal()

There is also a constructor that allows to create an UTC DateTime instead of creating a local DateTime and then converting to UTC.

answered Apr 02 '19 at 11:00

Günter Zöchbauer

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Zöchbaue: I updated my question. The results are the same. – Benjamin Apr 02 '19 at 11:07
I see you figured it out \o/ – Günter Zöchbauer Apr 02 '19 at 11:18
*Converting* a local `DateTime` object with `.toUtc()` won't make a difference since it would still represent the same moment in time. You would need to construct UTC `DateTime` objects with `DateTime.utc` with the desired values instead. – jamesdlin Feb 20 '22 at 19:57
@jamesdlin thanks for the hint. I assumed the values come from somewhere else anyway and I just created values to demonstrate, but I agree that this can cause confusion. – Günter Zöchbauer Feb 21 '22 at 13:07

Jama Mohamed · Answer 3 · 2023-03-11T13:05:56.620

Try this package, Jiffy uses the momentJs concept of date-time difference

You can see dicussion here https://github.com/moment/moment/pull/571

var aprilFirst = Jiffy.parseFromList([2019, 3, 30]);
var marchThirtyFirst = Jiffy.parseFromList([2019, 3, 31]);

aprilFirst.diff(marchThirtyFirst, Unit.day); // -1

var marchThirty = Jiffy.parseFromList([2019, 4, 1]);
var marchThirtyFirst = Jiffy.parseFromList([2019, 3, 31]);

marchThirty.diff(marchThirtyFirst, Unit.day); // 1
marchThirty.diff(marchThirtyFirst, Unit.hour); // 24
marchThirty.diff(marchThirtyFirst, Unit.month; // 0

score 1 · Answer 4 · answered Apr 09 '21 at 23:51

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2021 Based on answer

extension DateCalcs on DateTime {
  DateTime get dateOnlyUTC => DateTime.utc(this.year,this.month,this.day);
}

answered Apr 09 '21 at 23:51

Roddy R

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jamesdlin · Answer 5 · 2022-02-20T21:43:11.337

You've already figured out that you get an unexpected result due to your locale observing Daylight Saving Time. Duration internally stores a number of microseconds; Duration.days is measured in terms of 24-hour increments and not in terms of calendar days. From the DateTime documentation:

The difference between two dates in different time zones is just the number of nanoseconds between the two points in time. It doesn't take calendar days into account. That means that the difference between two midnights in local time may be less than 24 hours times the number of days between them, if there is a daylight saving change in between. If the difference above is calculated using Australian local time, the difference is 7415 days and 23 hours, which is only 7415 whole days as reported by inDays.

See https://stackoverflow.com/a/71198806/ for a more general version of Benjamin's answer that computes the difference in days between two dates, ignoring the time (and therefore also ignoring Daylight Saving adjustments and time zones).

Dart/Flutter DateTime difference inDays error for March 31 April 1

5 Answers5

2021 Based on answer

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