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 Florida, the written lease agreement is indeed a crucial document for outlining the rights of residential tenants and the responsibilities of landlords. Florida law allows landlords to include terms for late fees in the lease agreement, but these fees must be reasonable and related to the actual costs incurred by the landlord due to the late payment. The Florida Residential Landlord and Tenant Act does not specify a maximum amount for late fees, but they should not be punitive in nature. Additionally, Florida recognizes the implied covenant of good faith and fair dealing in contracts, which means that both landlords and tenants must act in a way that does not destroy the right of the other party to receive the benefits of the contract. A landlord charging excessive late fees or fees for marginally late payments could potentially be seen as acting in bad faith, especially if the lease does not explicitly state such strict terms. Tenants should read their lease agreements carefully before signing to understand their obligations and the penalties for late payments. It is advisable for tenants to seek clarification or negotiate terms that seem unreasonable or overly punitive.