Once I terminate my lease, will I owe the landlord any money?
Possibly. The law says that the tenant is responsible for one month's rent after s/he leaves the residence if the landlord has experienced and documented damages (loss of money) that are equal to at least one month's rent as a result of the tenant's early termination of the lease. This payment to the landlord would be due within 90 days of vacating your apartment/house. The landlord can keep your security deposit until you pay that one month’s rent or the landlord can use your security deposit to off-set the money you would owe him/her.1
What often happens is that the landlord holds onto the security deposit and returns it if s/he is able to quickly re-rent the apartment/house (and if the security deposit isn’t needed to repair physical damage to the unit). If the landlord cannot quickly re-rent the apartment/house, s/he keeps the security deposit in lieu of the rent payment due.
1 Colo. Rev. Stat. § 38-12-402(2)(b)