While we do often allow shorter than 12 month leases on our apartments, our published prices are typically based on 12 months rent. The increase for going with a shorter lease depends on the property but it’s typically:

Add $75/month for 6 month
Add $125/month for 3 month
Add $250/month for month to month.

The reason for this is there is a great deal of time and cost that goes into a new lease and a make ready between leases.  As such on shorter leases, those costs need to be amortized over a shorter period of time.