The difference that matters
GST law has nothing to say about quotations. A quotation, estimate or proforma is a commercial document — you can number it how you like, revise it five times, or throw it away. It creates no tax liability, it does not go into your GSTR-1, and your customer cannot claim input tax credit against it.
A tax invoice is the opposite on every count. It must carry the fields Rule 46 lists, take the next number in an unbroken series, appear in your return for that period, and it is what your customer's credit claim is built on.
| Quotation | Tax invoice | |
|---|---|---|
| Numbering | Yours to choose | Consecutive, unique per financial year, ≤ 16 characters |
| Tax liability | None | Yes |
| In your GSTR-1 | No | Yes |
| Customer's input credit | Not claimable | Claimable |
| Can be revised freely | Yes | No — corrections go through a credit or debit note |
When the liability actually starts
Not when you quote. For goods, your liability is tied to the issue of the invoice or the last date by which you were required to issue one. Taking an advance payment against an accepted quotation has its own treatment — for goods the tax is generally accounted for at invoice, while an advance for services is taxable when received, against a receipt voucher.
The practical consequence is simple: sending a quotation costs you nothing in tax, however large it is and however long it sits unanswered. Nothing is owed until the invoice exists.
What must change at conversion
- The number. The invoice takes the next number in the invoice series. It does not inherit the quotation's number, and the two series are independent of each other.
- The date. The invoice date is the date you issue it, not the date you quoted.
- The tax rates, if they have moved. A quotation from four months ago carries the rates of four months ago. The rate that applies is the one in force at the time of supply.
- The place of supply, if the delivery changed. Customers redirect deliveries after accepting a quote more often than you would think, and that can flip the whole document between IGST and CGST plus SGST.
What should carry over untouched
The customer and their GSTIN, every line with its description, HSN or SAC, quantity, rate and discount, and your own business details. This is the part worth automating: retyping fifteen lines to convert a quotation you already got right is how a quantity ends up transposed, and the customer notices on the invoice rather than the quote.
The two numbering series
Keep quotations and invoices in separate series. An invoice series has to be consecutive with no gaps, so if a quotation consumed a number in it, every quote you send and lose would leave a hole in your invoice numbering to account for.
Both series restart on 1 April. The financial year is part of the requirement — the series has to be unique within the year — so a format like INV/2026-27/0001 carries the year in the number itself. It also fits the 16-character limit exactly, which is worth checking if you plan to add a branch or location prefix.
How BahiSathi handles it
- Open the quotation you won. It keeps its own number and stays in your records exactly as you sent it. Converting does not consume or overwrite it.
- Convert it to a tax invoice. The customer, the lines, the quantities, the rates, the discounts and the place of supply all carry over. Nothing is retyped, so nothing is mistyped.
- Check what has moved on. Change anything the customer negotiated after the quote, and confirm the tax rates are still the ones in force today rather than the ones on the day you quoted.
- Issue it. That is the moment the invoice takes its number from the invoice series, and the moment the document becomes a tax invoice rather than an offer.
The quotation survives the conversion, so you keep the record of what you offered alongside what you eventually billed. The two series are maintained separately and both restart on 1 April on their own, and because the invoice number is reserved on our server at the moment you issue, a second device on the same account cannot take the same one.
A plain-language summary, not legal advice. Time-of-supply rules have more detail than fits here, particularly around advances; check your own case with your accountant.