Add/Subtract months/years to date in dart?

Okay so you can do that in two steps, taken from @zoechi (a big contributor to Flutter):

Define the base time, let us say:

var date = new DateTime(2018, 1, 13);

Now, you want the new date:

var newDate = new DateTime(date.year, date.month - 1, date.day);

And you will get

2017-12-13

You can use the subtract and add methods

 date1.subtract(Duration(days: 7, hours: 3, minutes: 43, seconds: 56)); 

 date1.add(Duration(days: 1, hours: 23)));

Flutter Docs:

Subtract

Add

Try out this package, Jiffy. Adds and subtracts date time with respect to how many days there are in a month and also leap years. It follows the simple syntax of momentjs

You can add and subtract using the following units

years, months, weeks, days, hours, minutes, seconds and milliseconds

To add 6 months

DateTime d = Jiffy().add(months: 6).dateTime; // 2020-04-26 10:05:57.469367
// You can also add you own Datetime object
DateTime d = Jiffy(DateTime(2018, 1, 13)).add(months: 6).dateTime; // 2018-07-13 00:00:00.000

You can also do chaining using dart method cascading

var jiffy = Jiffy().add(months: 5, years: 1);

DateTime d = jiffy.dateTime; // 2021-03-26 10:07:10.316874
// you can also format with ease
String s = jiffy.format("yyyy, MMM"); // 2021, Mar
// or default formats
String s = jiffy.yMMMMEEEEdjm; // Friday, March 26, 2021 10:08 AM