- Actual Sighting judged by Qadi, or Review Panel. (e.g., Bangladesh, India, Pakistan, Oman, Morocco, Trinidad)
- Moon born & moonset after sunset in Makkah. (e.g., S. Arabia, sometimes deviates for Ramadan, Shawwal, and Dhul-Hijjah)
- Follow Saudi Arabia. (e.g., Qatar, Kuwait, UAE, Bahrain, Yemen, Turkey)
- Moon Born & moon sets at least 5 minutes after sunset. (e.g., Egypt)
- News from neighbor countries. (e.g., New Zealand gets from Australia, and Suriname gets from Guyana)
- Follow first Muslim country that announces it. (e.g., Some Caribbean Islands)
- Criteria of age, or altitude, or sunset-moonset lag. (e.g., Algeria, and Tunisia)
- Age > 8 hours, altitude > 2°, elongation > 3°. (e.g., Malaysia, Brunei and Indonesia)
- Pre-calculated calendar. (Bohra, Ismaiili, and Ahmadiyyah [Qadiani] community in the world)
- No specific criterion! Decision varies year by year. (e.g., Nigeria)
This complexity in method worldwide carries over to the Western muslim community, of course, as muslim immigrants initially tend to adheres to the tradition of their homelands. But there is intense cross-fertilization between muslims in the West - something that occurs nowhere else. Ultimately it boils down to a personal judgement as to which method to use - who said the gates of ijtihad were closed?
Incidentally, it is also Rosh Hashana, so L'Shana Tovah! Another example of an Abrahamic convergence.