Getting a GST registration isn't optional once your business or services hit certain revenue figures. If you're selling goods, you generally have to register once your sales cross Rs 40 lakh in most places. But if your business is in one of those "special category" states, like many in the North-East or hilly areas, that limit drops to Rs 20 lakh. For folks providing services, the general rule is Rs 20 lakh, and again, Rs 10 lakh if you're in those special category states.