Most invoices that get sent back are not wrong about the money. They are missing a field. A buyer cannot claim input tax on an invoice that does not carry the right details, so their accounts team returns it, and you get paid a fortnight later than you should have been.
This is what a GST invoice needs to show, and why each part is there.
Your details as the supplier
Your registered business name, address and GSTIN have to appear exactly as they do on your registration. A shortened trading name or an old address is enough for a careful accounts team to query the document.
This is the part worth getting saved once in whatever you invoice with, because retyping it is how inconsistencies creep in across a year of invoices.
Your customer’s details
Name, address and, where they are registered, their GSTIN. That last one is not a formality. Without it on the invoice, a registered buyer cannot claim the tax they paid you, which turns your invoice into a cost for them rather than a wash.
You also need the place of supply, because that is what decides which taxes apply.
A serial number and a date
Invoice numbers must run in a consecutive series for the financial year. Not two series that overlap, not a number you skipped because a draft was abandoned, and never the same number twice.
Gaps and duplicates are among the first things an auditor looks for, because they suggest invoices that exist somewhere but not in the records.
What you actually sold
Each line needs a description, the quantity and unit, the rate, and the HSN or SAC code. Goods carry an HSN code, services carry a SAC code. Both are required for your GSTR-1 to file cleanly.
If you sell the same handful of things repeatedly, saving each one with its code and tax rate removes the most common source of error on an invoice, which is someone typing the code from memory.
The tax, shown separately
The taxable value and the tax have to be visible as separate figures, with the rate stated. A single total with tax folded in does not let the buyer account for it.
Which taxes appear depends on where your customer is:
| Supply | What you charge |
|---|---|
| Within your own state | CGST and SGST, each half the total rate |
| To another state | IGST at the full rate |
An 18% supply inside your state is 9% CGST plus 9% SGST. The same supply to a customer in another state is 18% IGST. Getting this backwards is common, and it is the customer’s state that decides it, not yours.
The omissions that cause the most trouble
- Missing HSN or SAC codes. The invoice looks fine to the customer but your GSTR-1 will not reconcile cleanly.
- The customer’s GSTIN left blank. They cannot claim the tax, so they will ask for a revised invoice.
- Tax folded into one total. The buyer has no way to record the tax component.
- A broken number series. Not a problem until it is, and by then it covers a whole year.
- The wrong tax type. CGST and SGST charged on an inter-state supply, or IGST charged locally.
If you are not GST-registered
You do not issue a GST invoice at all. Below the registration threshold you send a plain bill of supply with no tax on it, and you must not show GST you are not entitled to collect.
When you do register, the change is straightforward: add your GSTIN, apply the right rates to what you sell, and start a compliant number series. Nothing you sent before needs revisiting.
The practical takeaway
Almost every field above is something you enter once and reuse. Your own details, each customer’s GSTIN and state, and the code and rate against each thing you sell. Once those are saved, a compliant invoice takes about a minute and the fields that get queried are simply always there.
You can put together a compliant invoice right now with our free invoice generator, or check the arithmetic with the GST calculator. Neither asks you to sign up.
This article is general guidance, not tax advice. GST rules and rates change. Confirm anything specific to your business with your accountant.