The law
Income-tax Act 1961, Sec 54(1) (now Sec 82)
Individual or HUF; long-term residential house whose income is under 'house property'; buy a new house in India 1 year before or 2 years after the transfer, or construct within 3 years; exempt to the extent of the cost of the new houseSource
Income-tax Act 1961, Sec 54(1) (now Sec 82) proviso (two houses)
If the gain does not exceed ₹2 crore, the gain may be invested in two houses in India; option can be used only onceSource
Income-tax Act 1961, Sec 54(1) (now Sec 82; ₹10 crore cap, from AY 2024-25)
Cost of the new house above ₹10 crore is ignored, also for the CGAS depositSource
Income-tax Act 1961, Sec 54(1)(i) (now Sec 82) and (ii) (lock-in)
If the new house is sold within 3 years, its cost is reduced by the exempted gain (or taken as nil) when computing the gain on that saleSource
Income-tax Act 1961, Sec 54(2) (now Sec 82) and Capital Gains Accounts Scheme 1988
Gain not used before the Sec 263(1) (old Sec 139(1)) due date must be deposited in a notified bank scheme before filing; unused deposit is taxed in the year the 3-year period from transfer endsSource
Income-tax Act 1961, Sec 112 and 2(42A) (now Sec 2(101))
Land or building held over 24 months is long term; 12.5% without indexation for transfers on or after 23 July 2024; resident individual or HUF with property bought before 23 July 2024 may pay the lower of that and 20% with indexationSource
Income-tax Act 1961, Sec 50C (now Sec 78)
Stamp duty value replaces the agreed price if it exceeds 110% of it; agreement-date value applies if part payment was by banking mode on or before the agreementSource
Income-tax Act 1961, Sec 49(1) (now Sec 73)
For an inherited or gifted house, cost is the previous owner's cost plus improvementsSource
Income-tax Act 2025, Sec 82 (corresponds to old Sec 54)
From tax year 2026-27 the house-to-house exemption is Sec 82; Sec 50C becomes Sec 78 and Sec 49 becomes Sec 73Source
Government fee
No government fee to claim the exemption. Tax on any taxable balance at 12.5% (or 20% with indexation where chosen) plus surcharge and cess. Source: https://incometaxindia.gov.in/Tutorials/15-%20LTCG.pdf . Stamp duty on the new house is a state levy and is not part of this process.
Late fee or penalty
If the unused gain is not deposited in CGAS before the return due date, the exemption on that part is at risk (tribunals differ on a belated return). Source: https://bcajonline.org/journal/capital-gains-account-scheme-due-date-for-deposit/ . Late return fee under Sec 428 (old Sec 234F) of ₹5,000 (₹1,000 if income up to ₹5 lakh). Source: https://www.incometaxindia.gov.in/w/section-234f