The most important source of information about a residential tenant’s rights and a landlord’s responsibilities is the written lease agreement. Some landlords prefer oral agreements, but it is more common for them to require the tenant's signature on a written lease—and a written lease protects the tenant more than an oral agreement. Be sure to read the lease carefully before you sign it.

A residential landlord’s ability to charge late fees generally depends on the specific language in the written lease agreement; the state’s landlord-tenant laws that may limit the amount of late fees the landlord can charge and the circumstances in which they can be charged; and the state's contract law.

Contract law in most states recognizes an implied duty of good faith and fair dealing between parties to a contract, and a residential landlord who charges late fees because the tenant is an hour late paying the rent may be in breach of the landlord’s implied duty of good faith and fair dealing—unless, for example, the lease agreement specifies an hour (12:00 p.m.) of the day by which rent is due and states that time is of the essence.

In Iowa, the lease agreement is indeed a crucial document outlining the rights of residential tenants and the responsibilities of landlords. Iowa law allows landlords to use written or oral lease agreements, but written leases provide clearer evidence of the terms agreed upon by both parties and are generally more protective of tenant rights. Tenants should read and understand the lease before signing. Regarding late fees, Iowa Code section 562A.9(1) permits landlords to charge late fees if the fees are reasonably related to the expenses the landlord incurs as a result of the late payment. However, the fees must be outlined in the written lease agreement to be enforceable. Iowa's landlord-tenant law does not specify a maximum amount for late fees, but they must not be punitive in nature. Additionally, the concept of an implied duty of good faith and fair dealing is recognized in Iowa contract law, which means that landlords are expected to act fairly and not exploit situations to penalize tenants unreasonably. For instance, charging a late fee for rent that is only an hour late without a clear stipulation in the lease that time is of the essence could be seen as a breach of this duty. It is always advisable for tenants to review their lease agreements carefully and consult with an attorney if they have questions about their rights and obligations.