GST trips up more design studios than any bad client ever will. Not because designers are careless. Because interior design in India is a messy mix of pure service, goods, subcontracted labour, site travel, and advances that land in your account long before any work is billed. GST wasn't written with a boutique design studio in mind, so the edges are where people get hurt.
I've watched studio owners get a notice for something they didn't even know was a mistake. Usually it's small, boring stuff that piles up over a financial year. So here's a plain rundown of the seven that come up again and again, and how to stop them from becoming a problem at filing time or, worse, during an assessment.
If you want the fundamentals before we dig into mistakes, park this open in another tab: GST for Interior Designers in India: A Plain-English Guide. This post assumes you already know the basics and want to avoid the traps.
1. Using the wrong SAC code (or picking one at random)
This is the most common one. You raise an invoice, the accountant asks for a code, and someone just types in whatever was used last time. Interior design is a service, so it sits under a SAC (Services Accounting Code), not an HSN. Pure design and consultancy work generally falls under the professional/technical services family (the 9983 group), while a full turnkey job where you're supplying and installing goods behaves differently and can pull works-contract treatment.
Why it matters: your SAC code drives your GST rate and how the transaction reads to the department. If you're doing consultancy but billing it under a supply-of-goods logic, or mixing a turnkey works contract into a plain design invoice, your rate can be wrong and your GSTR filings stop matching reality.
The fix is boring but effective. Decide, per project, what you're actually selling:
- Pure design fees, drawings, 3D, consultancy, a service.
- Supply + install of furniture and finishes as one turnkey deliverable, closer to a works contract.
- A mixed job, split it cleanly on the invoice so each line carries the right code and rate.
Lock the correct SAC into your invoice template once, per service type, and stop deciding it fresh every month. Get this and the layout right and half your GST worries disappear, I've written up exactly how in How to Raise a GST-Compliant Invoice for Design Work.
2. Ignoring GST on client advances
Design runs on advances. Client signs, pays 40% upfront, and only then do you start ordering, drawing, chasing vendors. Here's the part people miss: for a supply of services, GST is due when you receive that advance, even though you haven't raised the tax invoice for the full scope yet.
So a ₹4,00,000 advance on a ₹10,00,000 project isn't just working capital sitting in your account. The tax on that advance is a liability the moment it hits, and you're expected to account for it in that period through a receipt voucher and pay the GST accordingly, then adjust when you raise the final invoice.
Where studios go wrong:
- They treat the advance as "not income yet, so no GST yet."
- They forget to issue a receipt voucher against the advance.
- They pay the tax only when the final invoice goes out, months later, and end up with interest for late payment.
This is genuinely fiddly, and it's worth getting exactly right because the money involved is large. I've broken down the mechanics separately in How to Handle Client Advances and GST the Right Way, read that one if advances are a big part of how you get paid, which for most studios they are.
3. Charging CGST+SGST when it should be IGST (and the other way round)
This is the interstate trap. A Mumbai studio designing a home in Pune, same state, so CGST + SGST. The same Mumbai studio designing a villa in Bengaluru, different state, and now you're often looking at IGST instead. Get it backwards and your invoice is wrong, your client's input credit gets messy, and reconciling GSTR-1 with what actually happened becomes a headache.
The catch is that for services, "which state" isn't always where your office is or even where the client lives. It's driven by the place of supply rules, and for work tied to immovable property, which a lot of interior work is, the place of supply can be the location of the property itself. That single rule flips a surprising number of invoices.
Don't guess this one. Genuinely, the place-of-supply logic for design services has enough edge cases that it deserves its own read: Place of Supply for Interior Design Services, Explained. The short version: figure out the correct place of supply first, and the CGST/SGST-vs-IGST question answers itself.
4. Blindly claiming input tax credit on everything
Your studio buys a lot. Samples, laptops, software subscriptions, site travel, client dinners, hoardings, the works. It's tempting to claim input tax credit on all of it. But ITC has blocked categories, and some of what a design studio spends on sits squarely in them or in a grey zone.
Two things bite people:
- Claiming ITC on stuff where credit is restricted or blocked, then having to reverse it later with interest.
- Claiming ITC that your supplier never actually reported, so it doesn't show in your GSTR-2B. If it's not in 2B, the department's view is you generally can't take it, no matter what your vendor's invoice says.
The habit that saves you: reconcile your purchase register against GSTR-2B every month before you finalise. If a vendor hasn't filed, chase them then, not eleven months later when you've forgotten which PO it was. And be honest about which expenses are genuinely eligible instead of claiming first and arguing later.
5. Threshold and registration confusion
The registration threshold for services is lower than a lot of people assume, and it's easy to cross it without noticing, especially once you land one or two big turnkey projects in a year. Some studios stay unregistered too long and then scramble. Others register, forget they've crossed into a bracket where they can't just casually collect without filing properly, and let returns slip.
There's also the interstate angle again: certain interstate supplies can require registration regardless of turnover. So the "I'm small, I don't need to bother yet" logic breaks the moment you take on an out-of-state project.
Practical stance: track your rolling turnover, not just this month's. If you're within striking distance of the threshold, register before you cross it rather than after. Registration is cheap. A backlog of unfiled returns plus penalties is not.
6. Filing late (or letting reconciliation drift)
GST is a monthly and quarterly rhythm, and design studios are terrible at rhythm because the work is lumpy. Big month, dead month, three invoices in one week, nothing for a fortnight. So returns slip. GSTR-1 goes in but GSTR-3B is late. The tax on that advance from point 2 is technically due but nobody paid it on time.
Late fees and interest are small per instance and enormous in aggregate. And a messy filing history is the thing that turns a routine query into a full assessment.
What actually helps isn't discipline, it's not relying on discipline. Bill from a system that already knows the GST treatment of each line, so the numbers you file are the numbers you invoiced, with nothing re-keyed by hand at month-end.
7. Treating advances as untracked cash instead of tracked liability
This is the quiet killer, and it overlaps with everything above. When an advance isn't tracked against a specific project, phase, and eventual invoice, two things happen. You lose money, because some of it never gets adjusted against a final bill and just evaporates into "general receipts." And you mishandle the GST, because you can't pay tax correctly on money you're not tracking.
I've seen studios genuinely surprised to find advances they collected, spent, and never invoiced against. It's not fraud. It's just that the payment came in over WhatsApp, went into the account, and nobody tied it to anything. I wrote a whole piece on this because it's so common: Untracked Advances: The Payment Leak Nobody Notices. Fix the tracking and the GST on advances mostly fixes itself, because now every rupee has a home.
The common thread
Notice something about all seven? None of them are exotic tax law. They're what happens when your quotes, invoices, advances, and vendor bills live in different places, a spreadsheet here, Tally there, a payment on WhatsApp, a PO in someone's email. The gaps between those places are where SAC codes get guessed, advances go untaxed, and IGST/CGST gets flipped.
That's the whole reason Designa keeps the quote-to-invoice chain in one place. Your quote carries the right SAC code and GST treatment from the start. When it becomes a GST invoice, the tax logic comes with it, CGST+SGST or IGST based on the actual place of supply, not a manual toggle someone forgets. Advances get recorded against the project so nothing goes untracked, and every payment you collect through Razorpay is tied to a specific client and job. Then it all syncs to Tally and Zoho Books, so your accountant is reconciling clean data instead of chasing you for context. One flat founding price, ₹2,299 + GST per year for the whole studio, up to 10 members, done-for-you onboarding and data migration, 7-day money-back.
You don't need to become a GST expert. You need a workflow that doesn't create these mistakes in the first place. Poke around the live demo at https://demo.designa.work, and when you're ready to stop losing sleep over month-end, grab the founding offer at https://go.designa.work.