“What if the rental discount requires payment even before moving in?” asked Yehudah. “For example, the landlord may demand that payment be made a month before the rental lease begins. The rationales you mentioned might not apply in this case.”
“There is, indeed, a dispute on this issue, but many authorities allow the prepayment discount even before the renter moves in,” answered Rabbi Dayan. “However, there must already be a binding commitment to the rental, either through a signed lease, kinyan sudar, etc. Some also suggest that the rental must be fit for renting at the time of the prepayment.” (Taz and Nekudos Hakesef 176:7; The Laws of Ribbis 11:14-22; Bris Yehudah 26:1 ftnt. 2)