There's a specific kind of pain I see in interior studios, and it happens at the exact moment you should be celebrating. The project is done, the client loved it, and now you have to send a bill, and you're staring at a Word template someone made three years ago wondering if it's even a valid GST invoice. The truth is that most studio invoices I see are almost right, which is worse than being obviously wrong, because "almost right" is what gets bounced by the client's accountant and stuck for two weeks. So let me lay out the right GST invoice format for interior designers, the structure a tax invoice must follow, and how to lay out the messy goods-plus-services reality of interior work cleanly.
First, know which document you're actually raising
Before format, get the document type right, because studios blur these constantly and it causes real confusion. A quote or estimate is not an invoice, it's a proposal. A proforma invoice looks like a bill but has no tax-invoice standing, it's a "this is what it will cost" preview. A tax invoice is the real, legal, GST-carrying document that lets your client claim input credit. And if you ever supply something exempt or you're under the composition scheme, that's a bill of supply, not a tax invoice.
The reason this matters for format is that only the tax invoice has the mandatory-field rules, and only the tax invoice supports your client's credit. So when you're billing taxable design work, you're raising a tax invoice, and it must say "Tax Invoice" at the top, not "Bill", not "Invoice", not "Estimate". The definitions are set out on the CBIC-GST site if you want the letter of the law.
The anatomy of a compliant tax invoice
Let me give you the layout as an interior designer should see it, top to bottom, because a tax invoice is really three zones stacked. The header zone identifies the parties and the document. The body zone itemises what you supplied and the tax on it. The footer zone totals everything and signs it off.
| Zone | What it must carry |
|---|---|
| Header | "Tax Invoice", unique serial number, date, your name, address and GSTIN, client name and address (and their GSTIN if registered) |
| Body | Each line with description, SAC or HSN code, quantity, rate, taxable value, then the tax rate and amount split by CGST/SGST or IGST |
| Footer | Total taxable value, total tax, grand total in figures and in words, place of supply, reverse-charge status, and your signature |
If you want the field-by-field walkthrough with the reasoning behind each one, I wrote that as how to raise a properly GST-compliant invoice for design work, and this post is the companion that focuses on how you actually lay it out and keep the series clean.
The invoice number series is a format decision, and studios botch it
Here's a formatting rule that carries more weight than people expect. Your tax-invoice numbers have to run as one continuous, sequential series across the financial year, with no gaps and no duplicates. That sounds trivial until you realise how many studios break it by hand, they start a new numbering per client, they skip numbers, they reuse an old one, or they raise a "corrected" invoice on the same number as the original.
A good series design is boring on purpose, something like DES/2026-27/0001 running upward, one unbroken chain. The prefix can carry your studio initials and the financial year, and then the running number just increments. Why does it matter? Because a broken series is one of the first things flagged in scrutiny, and a gap invites the question "what happened to invoice 0043", which you never want to be answering. Design the series once, then never touch the logic again.
Laying out the goods-plus-services mess cleanly
This is where interior invoices are genuinely harder than, say, a consultant's invoice, because a single project mixes a design service with supplied goods, and those don't share a code or always a rate. The wrong instinct is to lump everything into one line at one rate and hope, and that's exactly what gets queried.
The clean layout is line-by-line honesty. Your design fee sits on its own line with the interior-design SAC and 18%. Each supplied item, the wardrobe, the sofa, the tiles, the lighting, sits on its own line with its own HSN code and its own rate. When you're unsure which code a particular item takes, an HSN/SAC code lookup resolves it before you commit it to the invoice. This line-by-line format is more work up front and far less work later, because when the client's accountant reviews it, every line justifies itself and nothing needs explaining.
A format check before you send any tax invoice
- The document is clearly titled "Tax Invoice"
- The serial number continues your unbroken series for the year
- Your GSTIN and the client's GSTIN (if registered) are both present
- Design fee and supplied goods sit on separate, correctly-coded lines
- The tax split matches the place of supply, CGST/SGST or IGST
- The total appears in both figures and words, and it's signed
Where the format changes: exports and change orders
Two situations bend the standard format, and you should know them so you don't get caught. The first is overseas work, because an export invoice carries different flags, often no tax with an LUT reference instead, and the place-of-supply field does heavy lifting. I covered that whole scenario in LUT and GST for overseas and NRI design clients, and the format point is simply that the same template has to flex for it.
The second is when the scope changes mid-project, which in interiors is basically always. A change order doesn't get bodged onto the original invoice, it usually flows through a supplementary document, and getting that right is its own small discipline that I unpacked in handling GST on design change orders. The format lesson is that your numbering and your document types have to accommodate revisions cleanly rather than by overwriting history.
Keeping all of this straight by hand is where studios lose evenings, and it's why steady bookkeeping habits for an interior studio pay off, because a tidy invoice series and clean records are two sides of the same coin. You can register and manage your GSTIN details on the official GST portal so the identity fields on your template are always accurate.
Stop rebuilding the template every time
Here's my honest take after seeing too many 11pm invoice scrambles. The format of a tax invoice is fixed and knowable, which means it should never be a fresh act of typing. The studios that suffer are the ones rebuilding the layout in Word for every project, retyping codes, guessing the tax split, and hoping the serial number is right. The studios that don't suffer are the ones where the approved quote becomes the invoice automatically, with the format, the codes and the series all handled by the system.
That's exactly why I built billing into Designa the way I did, so the layout is correct by construction, the series stays continuous on its own, and the goods-versus-service lines carry the right codes without you thinking about it. Understanding how Designa's one flat rupee price for the whole studio works makes the case on its own, because getting compliant invoicing shouldn't be an expensive per-seat add-on.
Frequently asked questions
What must a GST invoice for interior design include?
It must be titled "Tax Invoice" and carry a unique serial number, the date, your GSTIN and the client's, a line-by-line description with SAC or HSN codes, the correct tax split, and totals in figures and words with a signature.
Is a quotation the same as a tax invoice?
No, a quote or proforma is only a proposal or preview with no tax standing, whereas a tax invoice is the legal GST document that lets your client claim input credit.
How should I number my interior design invoices?
Use one continuous, sequential series for the financial year with no gaps or duplicates, typically a prefix with your initials and the year followed by a running number.
How do I invoice a project that mixes design fees and furniture?
Put the design fee on its own line with the interior-design SAC at 18%, and each supplied item on its own line with its own HSN code and rate, rather than lumping everything into a single line.
Get the format right once and every future invoice is a two-minute job instead of a two-hour worry. See a correct tax invoice generated from an approved quote at demo.designa.work, and when you want your whole studio on one flat founding price billed in rupees with unlimited free client logins, the founding offer is at go.designa.work.