how to subtract dates in flutter

 //the birthday's date
 final birthday = DateTime(1967, 10, 12);
 final date2 = DateTime.now();
 final difference = date2.difference(birthday).inDays;

int sum = [1, 2, 3].fold(0, (sum, current) => sum + current); // 6
int sum = [1, 2, 3].fold(0, (p, c) => p + c); // 6

Jiffy("2011-10-31", "yyyy-MM-dd").fromNow(); // 8 years ago
Jiffy("2012-06-20").fromNow(); // 7 years ago

var jiffy1 = Jiffy()
    ..startOf(Units.DAY);
jiffy1.fromNow(); // 19 hours ago

var jiffy2 = Jiffy()
    ..endOf(Units.DAY);
jiffy2.fromNow(); // in 5 hours

var jiffy3 = Jiffy()
    ..startOf(Units.HOUR);
jiffy3.fromNow(); 

var jiffy1 = Jiffy()
      ..add(duration: Duration(days: 1));
jiffy1.yMMMMd; // October 20, 2019

var jiffy2 = Jiffy()
    ..subtract(days: 1);
jiffy2.yMMMMd; // October 18, 2019

//  You can chain methods by using Dart method cascading
var jiffy3 = Jiffy()
     ..add(hours: 3, days: 1)
     ..subtract(minutes: 30, months: 1);
jiffy3.yMMMMEEEEdjm; // Friday, September 20, 2019 9:50 PM

var jiffy4 = Jiffy()
    ..add(duration: Duration(days: 1, hours: 3))
    ..subtract(duration: Duration(minutes: 30));
jiffy4.format("dd/MM/yyy"); // 20/10/2019


// Months and year are added in respect to how many 
// days there are in a months and if is a year is a leap year
Jiffy("2010/1/31", "yyyy-MM-dd"); // This is January 31
Jiffy([2010, 1, 31]).add(months: 1); // This is February 28