Can my security deposit go towards my last month's rent?
If all or part of your security deposit is called "last month's rent" on your lease or rental agreement, then applying this amount to your last month's rent is in agreement with the lease terms. If part of your deposit was not specifically for last month’s rent, you are supposed to pay rent the last 30 days you are there (even when the security deposit is larger than or equal to one month’s rent).
However, if you think there will be problems getting your landlord to return the security deposit, you may choose to use your deposit towards your last month’s rent. You may explain in a note and keep a copy that you need your money for moving expenses, and that you intend to leave the place clean (you may even offer to have the landlord inspect right then to look for damage).