java.time
Use the java.time classes built into Java 8 and later.
LocalDate now = LocalDate.now();
LocalDate epoch = LocalDate.ofEpochDay(0);
System.out.println("Days: " + ChronoUnit.DAYS.between(epoch, now));
System.out.println("Weeks: " + ChronoUnit.WEEKS.between(epoch, now));
System.out.println("Months: " + ChronoUnit.MONTHS.between(epoch, now));
Output
Days: 16857
Weeks: 2408
Months: 553