A Dart package for configuring date-repetition patterns (e.g. "bi-weekly", "the 10th of every month", "every three years on June 1st", etc.) and finding the DateTime objects that lie on the pattern.


  • Configure moderately complex date-repetition patterns
  • Create lists of DateTime objects that follow the pattern
  • Determine if any given DateTime object follows the configured pattern

Getting started

Simply download the package and import it into your project to begin using.


Configure a DateInterval object (e.g. bi-weekly, starting on January 1st, 2020)

final DateInterval interval = DateInterval(
    startDate: DateTime(2020, 01, 01), // set the first day of the interval
    interval: Intervals.weekly, // set the interval type
    period: 2, // set the period (i.e. how many [interval]s between each occurrence)

Create a list of DateTime objects that fall on the interval

Using the example bi-weekly object:

final Iterable<DateTime> dates = interval.getDatesThrough(DateTime(2020, 02, 01));
    DateTime(2020, 01, 01),
    DateTime(2020, 01, 15),
    DateTime(2020, 01, 29)

Determine if any given DateTime lies on the interval

Using the example bi-weekly object:

final DateTime fifteenthOfJanuary = DateTime(2020, 01, 15);
final bool isOnInterval = interval.includes(fifteenthOfJanuary);
expect(isOnInterval, isTrue); // true

Additional Information

Some special rules apply for the Intervals.monthly interval type. Since it's possible to set up an interval for the "31st of every month," but not every month has 31 days, the DateInterval will look for the "closest possible date."

What this means is that, if you have a rule for the "31st of every month" (see example below), it will count the 28th of February, the 31st of March, the 30th of April, etc. all as lying on the interval.

final DateInterval lastOfTheMonth = DateInterval(
  startDate: DateTime(2020, 01, 31),
  interval: Intervals.monthly,
  period: 1,

bool isValidDate = lastOfTheMonth.includes(DateTime(2020, 02, 29)); // leap year
// isValidDate: true

isValidDate = lastOfTheMonth.includes(DateTime(2020, 03, 31));
// isValidDate: true

isValidDate = lastOfTheMonth.includes(DateTime(2020, 04, 30));
// isValidDate: true

final DateInterval almostTheLastOfTheMonth = DateInterval(
  startDate: DateTime(2020, 01, 30),
  interval: Intervals.monthly,
  period: 1,

isValidDate = almostTheLastOfTheMonth.includes(DateTime(2020, 02, 29)); // leap year
// isValidDate: true

isValidDate = almostTheLastOfTheMonth.includes(DateTime(2020, 03, 31));
// isValidDate: false

isValidDate = almostTheLastOfTheMonth.includes(DateTime(2020, 04, 30));
// isValidDate: true