Progress Billing for Long Projects: Retention, GST, and Sign-offs

Progress billing for long projects in India: handling retention amounts, GST per stage, customer sign-off, and final settlement.

What Progress Billing Solves

Construction, infrastructure, manufacturing contracts, and long IT implementations stretch over months or years, making single-shot billing impractical. Progress billing splits the contract into measurable stages — foundation, structure, plastering, finishing — and invoices each stage as completed. This funds the contractor's ongoing costs (labour, materials, subcontractors) while giving the buyer visibility into progress. Unlike fixed milestone billing, progress billing typically uses percentage-of-completion measured by engineer or surveyor certificates.

Retention Amount Mechanics

Most progress billing contracts include a retention clause — typically 5-10% of each bill is withheld by the buyer until project completion plus a defects liability period (often 12 months after handover). The retention protects the buyer if defects emerge after handover. The contractor invoices the gross amount but receives the gross minus retention; the retained amount sits as a receivable until release. GST is charged on the full invoice value including the retained portion because supply has been made, regardless of when cash is received.

GST and Time of Supply Per Stage

Each stage invoice triggers GST liability based on the earlier of invoice date, payment date, or completion of that stage. For construction services, GST is typically 18% (or 5% for affordable housing with specific conditions). The retention amount's GST is also paid upfront — you cannot defer GST on retention to the date of release. This timing creates a working capital strain in long projects, which is why some contractors negotiate retention as a separate non-invoice security deposit.

Customer Sign-off and Disputes

Each progress bill should be backed by a measurement sheet, photographs of completed work, and a signed certification from the buyer's engineer or project manager. Without sign-off, the invoice is "pending certification" and many large buyers won't process payment. Building this evidence trail into your weekly workflow — rather than scrambling at month-end — is the difference between a smoothly run long project and one with constant payment disputes. Include a deemed-certification clause in the contract for situations where the buyer goes silent.

Managing Progress Bills in BillBabu

BillBabu lets you create a master contract with retention percentage, project stages, and certified-value tracking. Each progress bill is generated against an approved stage with GST on the full value, while the retention is tracked as a separate receivable in the customer ledger. When the defects liability period ends, a final retention release invoice closes out the contract cleanly with all amounts reconciled.

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