It is a good idea to NOT have the security deposit and the rental amount the same. As a landlord, I want tenants to understand that they are entirely different things, that they will get back their security deposit, with interest, if they turn the place back over to me in the same condition as in which they received it. And I don't want them to think they can use it as the last month's rent. If I get into that habit, I could inspect a place after they vacate and find damage done and will no longer have the security with which to repair it. It is important to make these things absolutely clear at the beginning of the tenancy.