Flutter: Find the number of days between two dates

I currently have a user's profile page that brings out their date of birth and other details. But I am planning to find the days before their birthday by calculating the difference between today's date and the date of birth obtained from the user.

User's Date of Birth

And this is today's date obtained by using the intl package.

Today's date

I/flutter ( 5557): 09-10-2018

The problem I am facing now is, How do I calculate the difference in days of these two dates?

Are there any specific formulas or packages that are available for me to check out?

You can use the difference method provide by DateTime class

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

UPDATE

Since many of you reported there is a bug with this solution and to avoid more mistakes, I'll add here the correct solution made by @MarcG, all the credits to him.

  int daysBetween(DateTime from, DateTime to) {
     from = DateTime(from.year, from.month, from.day);
     to = DateTime(to.year, to.month, to.day);
   return (to.difference(from).inHours / 24).round();
  }

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

This is the original answer with full explanation: https://stackoverflow.com/a/67679455/666221