GST for interior firms: milestone billing and a clean month-end

Interior and fit-out work is paid in stages, not one lump, which makes GST billing for interior designers its own small discipline. Get the milestone invoicing, the CGST/SGST/IGST split and a filing register right, and month-end stops being a scramble.

Why interior GST billing is stage-wise, not one big invoice

A residential fit-out or a commercial project runs over months and gets paid against agreed stages: booking, design sign-off, on-site start, mid-work, and handover. If you raise one invoice for the whole contract value, your GST liability, your cashflow and your client's expectations all fall out of step with the work actually done. So the honest way to bill an interior project is milestone by milestone, and the honest way to charge GST is on each milestone's taxable value as it is billed.

In Panzo a milestone is born from the deal's payment plan, materialises on the project when the deal is won, and stays editable in one place, the deal, while Finance shows the same schedule live. A permitted user can adjust an unbilled milestone's amount, date or name, or add an ad-hoc line for a retention or change order. Any milestone that has been invoiced or collected locks, so the accounting cannot be broken after the fact.

• Each stage you bill becomes one invoice, tied to the deal it came from.
• Approving the final quote re-slices the remaining unbilled milestones to the agreed value.
• An approved change order adds its own milestone, billed on approval.
• A running milestones-total versus project-value check keeps the schedule honest.

Getting the GST computation right: CGST/SGST vs IGST

The part firms get wrong by hand is the tax split. On every customer invoice, Panzo computes the GST for you and decides the split from the place of supply, not from a guess. Same-state supply splits the tax into CGST plus SGST; an inter-state supply becomes a single IGST line. That intra versus inter decision is resolved from the two GSTIN state codes, your studio's and the customer's, and it defaults to intra-state rather than ever silently applying a higher inter-state charge.

A single mode also decides both the maths and how the bill reads: GST worked backward out of an inclusive amount, added on top of an exclusive amount, or none at all for an unregistered or composition customer. Once you raise the invoice, the numbers are frozen onto it, so a later rate change never rewrites a bill the client already has.

How to keep a clean month-end with a filing register

The point of getting each invoice right is that the month closes itself. Panzo's GST and Compliance register rolls every invoice up GSTR-1 style, period by period: taxable value, CGST, SGST, IGST and output tax on sales. It then nets that output tax against input tax on your posted vendor bills to show Net payable for the filing month. After Care service invoices fold into the same register, so nothing taxable is quietly left out.

1. Bill each stage as it is earned

   Raise the milestone invoice when the stage is reached. The GST is computed and frozen at that moment, in the right split.

2. Post your vendor bills through the month

   Vendor invoices with three-way match carry the input tax you will net against sales.

3. Read the register period by period

   Open the GST and Compliance register for the filing month and check taxable value, the tax heads and output-versus-input netting.

4. File from a reconciled Net payable

   The register hands you a GSTR-1-style view and the Net payable figure, so you file from numbers that already tie out instead of rebuilding them in a spreadsheet.

Tie billing to cashflow and margin, not just tax

Because every invoice is a milestone and every milestone belongs to a project, the same numbers feed a live per-project profit and loss and a clear view of the cash you can actually see. Revenue is the contracted milestone value; cost is posted vendor bills plus site purchases plus approved reimbursements. Collections run through a maker-checker flow with WhatsApp payment reminders on overdue milestones, so chasing money does not depend on someone remembering to send a message.

That connection matters for margin too. If you priced the project properly at quotation and then held that price through to billing, the milestone values you invoice are the same ones your P&L expects, so GST, cash and margin all read from one source. When a project finishes, the billing schedule should be fully drawn down by the time you run your handover checklist, with no stray unbilled stage left behind.

None of this replaces your accountant or a full ledger; Panzo is operational finance, not a double-entry accounting package. What it removes is the manual GST arithmetic on every interior milestone and the month-end reconstruction of what you billed. See how the money side fits together on the Features page, and check the pricing plans, all flat per workspace and exclusive of GST.