Prorating the rent after the lease expires

[Brendan Moore]

My current tenant's lease ends in a month because they are buying a house. They are not sure when exactly the closing date will be but it could be sometime in the following month after the lease ends. They want to know if they could prorate the rent for the following month. They have been good tenants for the two years they were there so should I say yes or charge them a full month's rent? Any advice would be great. Thanks!