The simplest approach is to use ChronoUnit#between
method:
DateTimeFormatter formatter = DateTimeFormatter.ofPattern( "MMMM dd, yyyy", Locale.US );
LocalDate d1 = LocalDate.parse( "May 28, 2019", formatter );
LocalDate d2 = LocalDate.parse( "September 02, 2020", formatter );
long diff = ChronoUnit.MONTHS.between( d1, d2 ); // 15 full months
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solved Subtracting months in Java [closed]