Flutter - How to find difference between two dates in years, months and days?

I think it is not possible to do exactly what you want easily with DateTime. Therefore you can use https://pub.dev/packages/time_machine package that is quite powerful with date time handling:

import 'package:time_machine/time_machine.dart';

void main() {
  LocalDate a = LocalDate.today();
  LocalDate b = LocalDate.dateTime(DateTime(2022, 1, 2));
  Period diff = b.periodSince(a);
  print("years: ${diff.years}; months: ${diff.months}; days: ${diff.days}");
}

for hours/minutes/seconds precision:

import 'package:time_machine/time_machine.dart';

void main() {
  LocalDateTime a = LocalDateTime.now();
  LocalDateTime b = LocalDateTime.dateTime(DateTime(2022, 1, 2, 10, 15, 47));
  Period diff = b.periodSince(a);
  print("years: ${diff.years}; months: ${diff.months}; days: ${diff.days}; hours: ${diff.hours}; minutes: ${diff.minutes}; seconds: ${diff.seconds}");
}

What you are looking for is the Dart DateTime class You can get close to what you want in moment.js with

main() {
  var a = DateTime.utc(2015, 11, 29);
  var b = DateTime.utc(2007, 06, 27);

  var years = a.difference(b);
  print(years.inDays ~/365);

}

There is no inYears or inMonths option for DateTime though that's why the year is divided in the print. the difference function returns the difference in seconds so you have to process it yourself to days.

You can calculate from the total number of days:

void main() {
  DateTime a = DateTime(2015, 11, 29);
  DateTime b = DateTime(2007, 06, 27);
  int totalDays = a.difference(b).inDays;
  int years = totalDays ~/ 365;
  int months = (totalDays-years*365) ~/ 30;
  int days = totalDays-years*365-months*30;
  print("$years $months $days $totalDays");
}

Result is: 8 5 7 3077

You could write an extension on duration class to format it:

extension DurationExtensions on Duration {
  String toYearsMonthsDaysString() {
    final years = this.inDays ~/ 365
    // You will need a custom logic for the months part, since not every month has 30 days
    final months = (this.inDays ~% 365) ~/ 30
    final days = (this.inDays ~% 365) ~% 30

    return "$years years $months months $days days";
  }
}

The usage will be:

final date1 = DateTime()
final date2 = DateTime()
date1.difference(date2).toYearsMonthsDaysString()

You can use Jiffy Package for this like this

var jiffy1 = Jiffy("2008-10", "yyyy-MM");
var jiffy2 = Jiffy("2007-1", "yyyy-MM");

jiff1.diff(jiffy2, Units.YEAR); // 1
jiff1.diff(jiffy2, Units.YEAR, true);

the answer is yes, you can easilly achieve it with DateTime class in Dart. See: https://api.dart.dev/stable/2.8.3/dart-core/DateTime-class.html

Example

void main() {
  var moonLanding = DateTime(1969,07,20)
  var marsLanding = DateTime(2024,06,10);
  var diff = moonLanding.difference(marsLanding);

  print(diff.inDays.abs());
  print(diff.inMinutes.abs());
  print(diff.inHours.abs());
}

outputs: 20049 28870560 481176

final firstDate = DateTime.now();
final secondDate = DateTime(firstDate.year, firstDate.month - 20);

final yearsDifference = firstDate.year - secondDate.year;
final monthsDifference = (firstDate.year - secondDate.year) * 12 +
    firstDate.month - secondDate.month;
final totalDays = firstDate.difference(secondDate).inDays;

Simple approach, no packages needed.

I created my own class for Gregorian Dates, and I created a method which handle this issue, it calculates "logically" the difference between two dates in years, months, and days... i actually created the class from scratch without using any other packages (including DateTime package) but here I used DateTime package to illustrate how this method works.. until now it works fine for me...

method to determine if it's a leap year or no:

    static bool leapYear(DateTime date) {
    if(date.year%4 == 0) {
      if(date.year%100 == 0){
        return date.year%400 == 0;
      }
      return true;
    }
    return false;
  }

this is the method which calculates the difference between two dates in years, months, and days. it puts the result in a list of integers:

     static List<int> differenceInYearsMonthsDays(DateTime dt1, DateTime dt2) {
    List<int> simpleYear = [31,28,31,30,31,30,31,31,30,31,30,31];
    if(dt1.isAfter(dt2)) {
      DateTime temp = dt1;
      dt1 = dt2;
      dt2 = temp;
    }
    int totalMonthsDifference = ((dt2.year*12) + (dt2.month - 1)) - ((dt1.year*12) + (dt1.month - 1));
    int years = (totalMonthsDifference/12).floor();
    int months = totalMonthsDifference%12;
    late int days;
    if(dt2.day >= dt1.day) {days = dt2.day - dt1.day;}
    else {
      int monthDays = dt2.month == 3
          ? (leapYear(dt2)? 29: 28)
          : (dt2.month - 2 == -1? simpleYear[11]: simpleYear[dt2.month - 2]);
      int day = dt1.day;
      if(day > monthDays) day = monthDays;
      days = monthDays - (day - dt2.day);
      months--;
    }
    if(months < 0) {
      months = 11;
      years--;
    }
    return [years, months, days];
  }

the method which calculates the difference between two dates in months, and days:

static List<int> differenceInMonths(DateTime dt1, DateTime dt2){
    List<int> inYears = differenceInYearsMonthsDays(dt1, dt2);
    int difMonths = (inYears[0]*12) + inYears[1];
    return [difMonths, inYears[2]];
  }

the method which calculates the difference between two dates in days:

static int differenceInDays(DateTime dt1, DateTime dt2) {
    if(dt1.isAfter(dt2)) {
      DateTime temp = dt1;
      dt1 = dt2;
      dt2 = temp;
    }
    return dt2.difference(dt1).inDays;
  }

usage example:

void main() {
  DateTime date1 = DateTime(2005, 10, 3);
  DateTime date2 = DateTime(2022, 1, 12);
  List<int> diffYMD = GregorianDate.differenceInYearsMonthsDays(date1, date2);
  List<int> diffMD = GregorianDate.differenceInMonths(date1, date2);
  int diffD = GregorianDate.differenceInDays(date1, date2);

  print("The difference in years, months and days: ${diffYMD[0]} years, ${diffYMD[1]} months, and ${diffYMD[2]} days.");
  print("The difference in months and days: ${diffMD[0]} months, and ${diffMD[1]} days.");
  print("The difference in days: $diffD days.");
}

output:

The difference in years, months and days: 16 years, 3 months, and 9 days.
The difference in months and days: 195 months, and 9 days.
The difference in days: 5945 days.

DateTime difference in years is a specific function, like this:

  static int getDateDiffInYear(DateTime dateFrom, DateTime dateTo) {
    int sign = 1;
    if (dateFrom.isAfter(dateTo)) {
      DateTime temp = dateFrom;
      dateFrom = dateTo;
      dateTo = temp;
      sign = -1;
    }
    int years = dateTo.year - dateFrom.year;
    int months = dateTo.month - dateFrom.month;
    if (months < 0) {
      years--;
    } else {
      int days = dateTo.day - dateFrom.day;
      if (days < 0) {
        years--;
      }
    }
    return years * sign;
  }

difHour = someDateTime.difference(DateTime.now()).inHours;
    difMin = (someDateTime.difference(DateTime.now()).inMinutes)-(difHour*60);

and same for years and days