Subletting is a real estate arrangement where a tenant leases their rental property or part of it to another individual, known as a subtenant. How Much Does a Sublease Cost?The average cost (i.e. Subletting, also known as subleasing, involves renting out a property or a portion of it that you are currently leasing, to a new tenant. A sublease agreement is a legal contract signed between a tenant and a third party allowing the latter to rent out the entire property or any part of it. Here's some language for a sample letter requesting sublet permission. Use it in part or full when submitting your proposal. The majority of co-ops allow you to only sublet for 2 years out of every 5 years provided you have hit the minimum residency requirement. Sublet and sublease are two different words for the same concept. The suffixes of each word, "let" and "lease," both mean to rent out a property.