Dr. Monzer Kahf, a prominent economist and counsellor, states: “The money you save for purchasing a house is yours and as long as you did not buy yet a house that money is subject to Zakah every lunar year at the rate of 2.5% due and payable on the day you complete every year (the first year begins from the day you acquired nisab). If you did not pay Zakah in the past, you have to calculate the past Zakah and pay it as soon as you can. As you know, delaying the payment of Zakah after its due date is sinful.
If in the last year, say now, you contracted a purchase of a house (i.e., you signed a sale agreement) and the amount of the contract that becomes by the contract a debt on you is due in a short period of time that makes such that you have to use those savings for the payment of the debt, then for this year only you may deduct the amount you assign to pay the debt from your Zakatable savings.”