1. What a GST invoice must contain
Your name, address and GSTIN; an invoice number that runs in a series and is never repeated; the date; the customer's name and, for B2B sales, their GSTIN; the HSN code, quantity, rate and taxable value of each item; CGST and SGST shown separately for a sale within your state, or IGST for one outside it; the total; and either your signature or a line stating that the invoice is computer generated. Leave any one of these out and it is not treated as a valid tax invoice.
2. How CGST and SGST are applied
Split the GST rate down the middle. Cement at 28% becomes CGST 14% plus SGST 14%. Steel at 18% becomes 9% plus 9%. A single bill can carry items at different rates, each line taking its own, and the totals are then added up. Doing this by hand is where most mistakes are made.
3. The difference between B2B and B2C
If the buyer has a GSTIN — a contractor, a builder or another shop — you are raising a B2B invoice, and their GSTIN has to appear on it for them to claim input tax credit. For an ordinary buyer building a house, it is B2C and no GSTIN is needed. The two are reported separately in GSTR-1, so keep the customer's GSTIN saved in your software.
4. Getting the invoice number series right
Start a fresh series each financial year, such as INV-2026-00001. Numbers must never repeat and never skip. This is exactly where handwritten billing goes wrong, with two bills carrying the same number. Software increments the number for you and the worry disappears.
5. Doing all of it in 30 seconds
In MaterialBill you pick the item and enter the quantity. CGST and SGST are applied at the correct rate, the HSN code prints, the number series runs itself, and B2B or B2C is decided from the customer's GSTIN. At month end the GST summary is one click away — send it to your CA and the return is filed.
6. Cancelling and correcting a bill
Tearing a page out of a bill book leaves a gap that has to be explained; the digital equivalent is deleting an invoice, and it causes the same problem. A bill raised in error should be cancelled rather than removed, so it stays in the series marked cancelled and the numbering has no hole in it. Where the sale happened but the amount changes — a return, a shortage, a rate corrected after the fact — the right document is a credit note against the original invoice, not an edit. That distinction matters because GST expects the trail, and because a bill somebody quietly changed is worth nothing when it is questioned.
7. What the bill has to carry to be valid
A tax invoice needs your name, address and GSTIN; the buyer's name, address and GSTIN for a B2B sale; a serial number from an unbroken series and the date; a description of the goods with HSN code, quantity and unit; the taxable value, the rate and the amount of tax split into CGST and SGST or IGST; the place of supply; and a signature or digital signature. Miss any of those and it is a slip rather than an invoice. The point of putting the rate and HSN code on the item is that all of it appears without anybody having to remember.