Misunderstanding of early release termination

[Steve Hollback]

In a lease it states if you want to leave early from the lease, “if you move out before your lease expires and you provide a 30 day notice you shall be liable for one additional month of rent and shall forfeit security deposit.” So my question is if you give the 30 day notice now do you just pay June’s rent or does that also mean you must pay July’s rent as well? And is this legal to do in NY if they already have another person to rent the apartment when you move out?