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.

Subtract your existing RERA carpet area from the carpet area offered in the new flat. That difference is your additional free area. Divide it by your old carpet and multiply by 100 for the percentage. Both figures must be RERA carpet, and the final sq.ft must appear in the PAAA.

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.

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 34. 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 Calculator

Common 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 34. 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.