What it is
Stamp duty is a state tax levied on the instrument of transfer — the sale deed itself — calculated as a percentage of the property's value, using whichever is higher between the guideline value and the stated sale consideration. It is paid before registration, typically through e-stamping or the registration department's payment system, and the deed cannot be registered without proof of payment. A separate registration fee, distinct from stamp duty, is also payable at the same time.
Why it matters when you buy
Stamp duty is usually the buyer's single largest upfront cost beyond the sale price itself, so budget for it alongside the registration fee before you commit to a purchase. Because it is calculated on the higher of guideline value and sale consideration, understating the sale price in the deed does not reduce it and can itself create legal problems. Confirm the exact amount payable with the sub-registrar office or your document writer before the registration appointment, since assessment can vary with property type and use.
Where you find it
You pay stamp duty through the e-stamping system linked to tnreginet.gov.in, or through authorized vendors, ahead of your registration appointment, and the payment challan or certificate is presented at the sub-registrar office as part of registering the sale deed. Keep the stamp duty receipt with your other title documents — it evidences that the deed was properly stamped, which matters if the transaction is ever scrutinized.