Last Month Rent collected at move-in, and making up difference

[Garen T.]

I have verbiage in my application, as well as the lease, that clearly states that at the time of acceptance, I require 1st month, last month, and a $500 deposit. This is not a problem and is very easy to understand the amount due at the time of move-IN....

Recently, a tenant gave me a nice 2 month notice that they are moving out. Since the time of move-in, rent has gone up. I responded noting that they would need to provide the difference between what they paid, and what the current rent amount is. Their response was that the verbiage in the lease clearly states that they already paid the "last month rent" and there was nothing in there that stated they needed to pay the difference. I looked at things, considered the fact that the small amount of rent difference means a great more to them than it means to me, and had to agree with them. I am not going to be forcing the issue to re-coup a couple hundred dollars. They found a flaw in my lease and a loophole, and are going to use it. I'm OK with this one tenant doing it. 

However, I would like to have language in my lease agreement that resolves this issue. I can either choose to keep the language the same, and essentially let them lock in a lower rental rate in their final month, or have some sort of language that states that they will have a final month due of the difference between what they paid, and the current rate. 

What have others done on this?

Thanks

[Bjorn Ahlblad]

Quote from @Bruce Woodruff:

First and last usually means 2 x the monthly rent at that time......?

 Plus the security deposit. We call it a move in fee and collect certified funds a few days prior to handing over the keys and move in inspection which we video with the tenant.