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

Answer 1

@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

Answer 2

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.

Answer 3

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

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

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

Jiffy(aprilFirst).diff(marchThirtyFirst, Units.DAY); // -1
// or
Jiffy([2019, 3, 30]).diff([2019, 3, 31], Units.DAY); // -1

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

Jiffy(marchThirty).diff(marchThirtyFirst, Units.DAY); // 1
Jiffy(marchThirty).diff(marchThirtyFirst, Units.HOUR); // 24
Jiffy(marchThirty).diff(marchThirtyFirst, Units.MONTH); // 0

Answer 4

2021 Based on answer

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