How to calculate the additional free area in your redevelopment offer
The extra area in a redevelopment offer is simple arithmetic, provided both carpet figures are measured on the same basis.
How do I work out the additional free area?
The sum is plain arithmetic. Take the carpet area offered in the new flat and subtract the carpet area of your present flat. Whatever remains is your additional free area in sq.ft. To turn it into a percentage, divide that difference by your old carpet area and multiply by 100. If your flat is 500 sq.ft and the offer is 650 sq.ft, the additional area is 150 sq.ft, or 30 per cent. Our additional area calculator does this for every flat type in your building at one go.
The entitlement rule depends on which regulation governs you
There is no single “extra area” formula. Three regimes run in parallel, and quoting the wrong one is the commonest error in Mumbai redevelopment:
| Your building | Regulation | What each member is entitled to |
|---|---|---|
| Cessed, Island City, existing before 30/09/1969 | 33(7) | The carpet you actually occupy, with a floor of 27.88 sq m (300 sq ft) and a ceiling of 120 sq m (1,292 sq ft) |
| Building in a MHADA housing scheme layout | 33(5) | Existing carpet +35%, minimum 35 sq m, plus a Table-A slab by plot size |
| Ordinary non-cessed society | 33(7)(B) | Additional FSI of 15% of existing BUA or 10 sq m per tenement, whichever is more |
Source: DCPR 2034 (sanctioned), Regulations 33(5), 33(7) and 33(7)(B).
Worked example — three cessed occupants, one building
A single-plot scheme, so no composite addition applies.
Occupant A occupies 18 sq m — below the floor, so A is lifted to 27.88 sq m.
Occupant B occupies 46 sq m — between floor and ceiling, so B gets 46 sq m.
Occupant C occupies 135 sq m — above the ceiling, so C is rehoused to 120 sq m free, and pays construction cost at that year’s ASR for anything beyond.
Join neighbouring cessed plots and every occupier gains: +8% carpet in a scheme of 2 to 5 plots, +15% at six or more.
That last line is the lever most cessed societies never use. Your own entitlement is largely fixed by what you already occupy — but the number of plots in the scheme is negotiable, and it moves both the incentive FSI (50% to 60% to 70%) and every member’s carpet.
Why can the percentage be misleading?
A percentage is only honest when both numbers rest on the same basis. Under RERA 2016, carpet area is the net usable floor area, excluding external walls, shafts and any exclusive balcony, verandah or open terrace, but including internal partition walls, and the sale agreement must state it. Many older societies still quote built-up or super built-up figures from an old agreement. Comparing an old built-up figure with a new RERA carpet figure will either flatter or spoil the offer. Convert first with the carpet to built-up converter, then compare like with like.
How much extra area should our plot support?
There is no standard answer, and anyone quoting one figure for all of Mumbai is guessing. What a plot can give depends on its FSI potential and the scheme it falls under, such as 33(7) and 33(7)(A) for old and cessed buildings, 33(5) for MHADA layouts, 33(9) for cluster and 33(14) for slum schemes, plus fungible compensatory area under Regulation 31(3) of DCPR 2034 and any TDR under Regulation 32. FSI is always plot-specific.
- Ask for the exact sq.ft, not only a percentage.
- Confirm the figure is RERA carpet.
- Have it written into the registered PAAA, flat by flat.
A number in a presentation binds nobody. The final sq.ft must appear in the Permanent Alternate Accommodation Agreement, alongside the registered Development Agreement. Where the reading of your plot or scheme is genuinely open to argument, take it to a chartered accountant and your society's solicitor before signing. Weigh the whole package with our offer comparison tool.
Work it out for your own society
Enter your old and new carpet figures and see the extra area in sq.ft and as a percentage, flat by flat.
Open the Additional Area CalculatorCommon questions
Is the additional area calculated on carpet or built-up area?
Always on carpet area, and specifically RERA carpet area. Under RERA 2016 this is the net usable floor area, excluding external walls, shafts and any exclusive balcony, verandah or open terrace, but including internal partition walls. If your old records show built-up or super built-up, convert them first, otherwise the percentage you calculate will be wrong.
Is there a standard percentage of extra area every society gets?
No. The free area a plot can support depends on its FSI potential, the incentive scheme it falls under, fungible compensatory area under Regulation 31(3) of DCPR 2034 and any TDR loaded under Regulation 32. FSI is always plot-specific. Treat any single universal figure quoted to you as marketing, not as a calculation.
Where must the agreed additional area be recorded?
In the Permanent Alternate Accommodation Agreement, in exact sq.ft, for your own flat, along with the registered Development Agreement. The Government of Maharashtra directive dated 4 July 2019 under Section 79A of the MCS Act 1960 expects both agreements to be registered. A figure shown only in a presentation or brochure gives you nothing enforceable.
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