When does a small business have to register for GST?

Registration is compulsory once your aggregate annual turnover crosses the threshold: ₹40 lakh for a supplier of goods only (₹20 lakh in some states) and ₹20 lakh for a supplier of services or of both goods and services. In special category states the limits are lower (₹20 lakh for goods and ₹10 lakh for services, with some exceptions).

Some businesses must register regardless of turnover, for example those making inter-state supplies of goods, e-commerce operators and sellers supplying through them (with limited exceptions), casual taxable persons, non-resident taxable persons, and persons liable to pay tax under reverse charge. You can also register voluntarily below the limit.

Thresholds differ by state and nature of supply, so confirm the limit applicable to you with your CA or on the GST portal.