1. When registration becomes compulsory
The general threshold for a supplier of goods is forty lakh of aggregate turnover in a financial year, and twenty lakh in the special category states — but several states apply a lower figure, and the threshold for services is different again. Aggregate turnover means all your supplies added together, not just the taxable ones. Because the exact limit that applies to you depends on your state and what you sell, confirm it with your CA rather than assuming, and confirm it again if you open a second location.
2. When you should register even if you need not
Registration is compulsory below the threshold in some situations — inter-state supply of goods, selling through an e-commerce operator, and a few others. Beyond that there is a commercial reason: a registered buyer cannot claim input credit on your bill if you are unregistered, so contractors, companies and institutions will often simply buy elsewhere. If a meaningful share of your customers are businesses, registering is a sales decision as much as a compliance one.
3. What you need to apply
PAN of the business or the proprietor, Aadhaar for authentication, a photograph, proof of the business address such as an electricity bill or rent agreement with a no-objection letter, bank account details, and for a firm or company the constitution documents. The application is made on the GST portal and, with Aadhaar authentication, registration is generally granted within a few working days unless the application is picked for physical verification.
4. What changes in your billing the next day
Your invoice must carry your GSTIN, the buyer's GSTIN for B2B sales, HSN codes, and tax split line by line into CGST and SGST for a sale inside your state or IGST for one outside it. Invoice numbering must run in an unbroken series for the financial year. You start collecting tax and you start claiming input credit on your purchases, which means purchase bills matter as much as sales bills from that day forward.
5. Returns, and the rhythm they impose
Registration brings monthly or quarterly returns depending on the scheme you are on — outward supplies in GSTR-1 and a summary with tax payment in GSTR-3B. Missing them attracts late fees that accrue daily and, past a point, blocks your e-way bill generation. The practical answer is not discipline but structure: if every bill and every purchase is recorded as it happens, the return is a report rather than a reconstruction.
6. The composition scheme, briefly
Below a turnover limit a small trader can opt for the composition scheme: a flat rate on turnover, quarterly payment and a simpler return. The trade-off is real — you cannot collect tax from customers, you cannot claim input credit, and you generally cannot make inter-state supplies. For a purely local retail counter it can suit; for anyone selling to businesses it usually does not. Ask your CA to work it out on your actual figures before choosing.