Which tax goes on a fee invoice, which SAC code to use, how to number invoices, and a worked stage-wise fee example — a practical guide for architects and interior designers.

Most architecture studios learn GST invoicing by getting an invoice sent back. A client's accounts team rejects it because the tax is split the wrong way, the SAC code is missing, or the invoice number repeats one from last year. None of this is difficult once it is laid out in one place. This guide covers what goes on a GST fee invoice for an Indian architecture or interior design practice, with a worked example for a stage-wise fee. It is a practical summary, not tax advice — confirm anything specific to your practice with your CA.

Do you need to register at all?

GST registration becomes compulsory for a service provider once aggregate turnover in a financial year crosses ₹20 lakh (₹10 lakh in the special category states). Many small practices register earlier anyway, because corporate and developer clients prefer to deal with a registered supplier and want the GSTIN on the invoice.

Your GSTIN is 15 characters: a two-digit state code, your 10-character PAN, an entity number, the letter Z by default, and a check character at the end. The first two digits matter more than people think — they are your state for every tax calculation that follows. A Pune studio's GSTIN starts with 27 (Maharashtra); a Bengaluru studio's with 29 (Karnataka).

The rate: 18%, split one of two ways

Architectural and interior design services are taxed at 18%. What changes from invoice to invoice is how that 18% is charged:

Intra-state supply — your studio and the place of supply are in the same state. Charge CGST 9% + SGST 9%. CGST goes to the Centre, SGST to the state.
Inter-state supply — the place of supply is in a different state. Charge IGST 18%.

The total is the same either way. The split is not cosmetic, though: tax paid under the wrong head is not simply moved across. If you charge CGST and SGST where IGST was due, you pay the IGST and then claim a refund of what you paid under the wrong head — a slow and avoidable exercise.

Place of supply: the one rule that decides the split

For most professional services, the place of supply is the location of the client. Architecture is a special case. Services directly in relation to immovable property — the IGST Act names architects and interior decorators explicitly — have their place of supply where the property is located.

In practice this rarely causes trouble, because the client and the site are usually in the same state. It matters in cases like these:

A Mumbai client commissions a farmhouse in Goa. The property is in Goa, so a Maharashtra studio is making an inter-state supply — IGST — even though the client lives in the same state as the studio.
A Bengaluru developer appoints a Pune studio for a project in Pune. The property is in Maharashtra, so the supply is intra-state — CGST + SGST — even though the client is in Karnataka.
Pure advisory work with no particular building — a feasibility opinion, a design competition entry — may fall under the general rule instead.

When the client and the site are in different states, settle the treatment with your CA before the first invoice goes out, and keep it consistent for the whole project.

Which SAC code to use

Every line on a services invoice carries a SAC code (Services Accounting Code). Architecture sits under heading 9983, "other professional, technical and business services". The codes a studio uses most:

998321 — architectural advisory services
998322 — architectural services for residential building projects
998323 — architectural services for non-residential building projects (offices, clinics, schools, retail)
998328 — landscape architectural services
998391 — specialty design services, including interior design

A house or apartment is 998322; a clinic or café fit-out designed as architecture is 998323; the interiors of either is usually 998391. If one appointment covers both the building and its interiors, many studios put them on separate lines with separate codes. Confirm the codes for your mix of work with your CA.

What a GST tax invoice must show

Rule 46 of the CGST Rules lists what a tax invoice must contain. For a design studio, that comes down to:

Your studio's name, address and GSTIN.
An invoice number — a consecutive serial of no more than 16 characters, using letters, numbers, hyphens and slashes, unique for the financial year.
The invoice date.
The client's name, address and GSTIN if they are registered. For an unregistered client — most individuals building a home — the name, address and state, at least where the invoice is ₹50,000 or more.
A description of the service and its SAC code.
The taxable value.
The tax rate and amount under each head: CGST and SGST, or IGST.
The place of supply, with the state name, for inter-state supplies.
Your signature or digital signature.

Two further things are not on that list but are standard practice. The total in words ("Rupees Two Lakh Twelve Thousand Four Hundred only") removes any doubt about the figure, and clients' accounts teams expect it. Your bank details save a round of follow-up emails.

Invoice numbering that survives an audit

The financial year runs from 1 April to 31 March, and the serial has to be unique within it. A simple format that fits the rules:

Prefix / financial year / running number — for example SRA/2026-27/0001, which is exactly 16 characters.
Keep the prefix to three letters or digits so the number never runs past 16.
Restart the running number on 1 April. SRA/2027-28/0001 cannot clash with SRA/2026-27/0001, because the year is in the number.
Don't skip or reuse numbers. If an invoice is wrong after it has gone out, issue a credit note against it rather than cancelling and reusing the number.

You can run more than one series (one per branch, say), as long as each one is consecutive and unique for the year.

When to raise a stage invoice

A fee paid in stages is tied to events — the end of concept design, the issue of working drawings. Where the appointment is treated as a continuous supply with payments linked to stages, the invoice is due on or before the date each stage is completed; otherwise, a services invoice is due within 30 days of the supply. Either way, the stage date drives the invoice date. Raising it weeks later, when the client finally signs off, pushes the tax date around and makes reconciliation harder. Agree in the appointment letter what "stage complete" means — a sign-off email, the issue of a drawing set — and invoice on that date.

A worked example: a stage-wise fee

Sharma Rao Architects is a Pune studio (GSTIN starting 27, Maharashtra). It is appointed to design a 3BHK residence in Pune for a total professional fee of ₹9,00,000 plus GST, split across the six stages of the work:

Concept — 10% = ₹90,000
Schematic design — 15% = ₹1,35,000
Design development — 20% = ₹1,80,000
Working drawings — 25% = ₹2,25,000
Tender — 5% = ₹45,000
Site supervision — 25% = ₹2,25,000

That split is a common one, not a rule — use whatever your appointment letter says. Over the project, GST adds ₹1,62,000, so the client pays ₹10,62,000 in all.

The design development invoice, client in Pune

The property is in Pune and the studio is in Maharashtra, so this is intra-state:

Invoice number: SRA/2026-27/0007
Line: Professional fee — design development (20%), SAC 998322, ₹1,80,000.00
CGST @ 9%: ₹16,200.00
SGST @ 9%: ₹16,200.00
Total: ₹2,12,400.00 — Rupees Two Lakh Twelve Thousand Four Hundred only

The same invoice for a project in Bengaluru

Now suppose the studio designs an identical house for a client in Bengaluru, on a plot in Bengaluru. The property is in Karnataka, the studio in Maharashtra, so this is inter-state:

Line: Professional fee — design development (20%), SAC 998322, ₹1,80,000.00
IGST @ 18%: ₹32,400.00
Place of supply: Karnataka (29)
Total: ₹2,12,400.00

The client pays the same amount. What changes is which head the tax sits under, and therefore where it shows up in your GSTR-1 and in the client's input tax credit. Get the head wrong and a registered client cannot claim their credit, which is usually when the invoice comes back.

Expenses you pass on to the client

Printing, travel and approval fees that you recover from the client are generally part of the value of your service and attract GST along with the fee. The exception is a payment you make purely as the client's agent — a municipal scrutiny fee paid in the client's name, for instance — which can stay out of the taxable value if the pure agent conditions are met. Ask your CA which of your usual recoveries qualify, and show them as separate lines either way.

TDS on your fee

Income-tax TDS is separate from GST, but it arrives on the same invoice. Companies and many other clients deduct TDS on professional fees under section 194J, typically at 10%. Where GST is shown separately on the invoice, TDS is deducted on the fee excluding GST. Expect ₹18,000 less in the bank against the ₹2,12,400 design development invoice above, and reconcile it against your Form 26AS. Government departments may also deduct GST TDS of 2% on larger contracts.

E-invoicing

B2B invoices must be generated as e-invoices, with an IRN from the invoice registration portal, once a business's aggregate turnover crosses ₹5 crore in any financial year. Most studios are well below that. If yours is approaching it, plan the switch with your CA before the year in which you cross it.

A short checklist before an invoice goes out

Is the GSTIN on the client record correct? A 15-character GSTIN has a check character, so a single typo makes it invalid.
Where is the property? That, not the client's address, decides CGST + SGST or IGST.
Is the SAC code right for this line — residential, non-residential or interiors?
Is the invoice number the next one in this financial year's series, and 16 characters or fewer?
Does the total in words match the figure?
Is the stage actually complete, and is today the right invoice date?

How ProjectSathi handles this

The Architecture & Interiors edition of ProjectSathi builds these rules into the invoice. Each project carries its fee split across the six stages, so the next stage's line is ready when you start an invoice. The tax is worked out as CGST + SGST or IGST by comparing your studio's state with the place of supply. The place of supply starts as the client's state, and you can set it to the property's state on any invoice — for example a Mumbai client building in Goa — with the split recalculated on the spot. SAC codes default from the project type, invoice numbers follow the prefix / financial year / serial format within 16 characters, GSTINs are validated as you type, the total is written in words, and the invoice downloads as a PDF. Mark it sent, then paid, and the project P&L and the client's portal page update with it.

You can try all of it in the demo: choose Architecture & Interiors, enter your studio's city (it sets your GST state), and raise an invoice for one of the sample projects. The step-by-step demo guide walks you through it, and the GST invoicing page has the detail.