Ask “what is the FSI on this plot?” and you will often get one figure back. That figure is the start of the calculation, not the answer.
Floor Space Index (FSI), often called Floor Area Ratio (FAR), connects permitted built-up area to plot area. But a feasibility model has to ask more than the base number: which area is counted, which additional rights are optional, what can actually be loaded on the site, and what does each option cost?
Mumbai shows the mechanism clearly
Mumbai’s Development Control and Promotion Regulations, 2034 (DCPR 2034) separates the zonal or basic FSI from other routes that can change the permitted built-up area. The regulation covers additional FSI on payment of premium, transferable development rights (TDR), and fungible compensatory area under their own eligibility, payment and cap conditions.
That distinction matters. Additional FSI on payment of premium is optional and site-specific; the regulation says it is granted on application, payment and use on the same plot. TDR is a credit created and used under a separate rule set, with generation, receiving-plot and utilisation conditions. Fungible compensatory area has its own conditions and premium treatment.
Why a single number misleads
An early feasibility estimate should state which of these layers it includes:
- base or zonal FSI;
- premium FSI, including its price and cap;
- TDR, including receiving-plot eligibility and loading limits; and
- fungible or excluded areas, where applicable.
Without that breakdown, two teams can use the same quoted FSI and reach different buildable areas, costs and underwriting results. The single figure was never the full development rule.
The general lesson
Mumbai’s mechanism is not a template to copy into another city. Premium rights, redevelopment incentives, transferable rights, road conditions and exclusions are local regulatory questions. A usable feasibility number therefore names the governing regulation, its retrieval date, included layers and unresolved approvals.
This is not legal or regulatory advice. For a live transaction or filing, confirm the current regulation and site conditions with the relevant sanctioning authority and qualified professionals.