Is it permissible to purchase real estate through an escalating installment plan over 240 months, knowing that the total value of the property will be much greater than its initial estimated value?

Installment sales are permissible, even if the price is higher than a cash sale, provided that the price is known and the installments are fixed, not exceeding what was agreed upon. The contract must be decisively concluded either for cash or for deferred payment. It is not permissible to stipulate installment interest separate from the immediate price, nor is it permissible to obligate the indebted buyer to pay an increase on the debt for late payment. If the estimated value was for the offer only, and the contract was concluded for a fixed, known amount where the price does not increase, then this is permissible. However, if the price is unknown at the time of writing the contract, and then the installments increase in accordance with market prices, this is impermissible due to the unknown price and uncertainty (gharar). As for increasing the installment value every six months, if this was known at the time of writing the contract and the total result is the same price agreed upon in the contract, then this is permissible. But if the increase is unknown and causes the price to exceed what was specified in the contract, or if the total price was not determined, then this is impermissible.