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 Missouri, the lease agreement is indeed a crucial document outlining the rights of tenants and the responsibilities of landlords. It is highly recommended for tenants to have a written lease, as it provides more security and clarity than an oral agreement. When it comes to late fees, Missouri law does not specifically cap the amount a landlord can charge, but the fees must be deemed reasonable and are typically enforceable if they are clearly stated in the lease agreement. The lease should outline when the rent is due, the amount of the late fee, and when the fee will be assessed. Additionally, under general contract law principles, both parties to a lease are expected to act in good faith and fair dealing. A landlord charging excessive late fees or fees for minimal lateness without clear terms in the lease could potentially be seen as acting in bad faith. Tenants should carefully review their lease agreements for such terms before signing to ensure they understand their obligations and the potential consequences of late rent payments.