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 Wisconsin, the written lease agreement is indeed a crucial document outlining the rights of tenants and the responsibilities of landlords. Wisconsin law allows landlords to include terms for late fees in the lease agreement, but these fees must be reasonable and are regulated under Wisconsin Statute 704.17(4). This statute stipulates that any late fees charged must be outlined in the lease and cannot constitute a penalty for nonpayment or late payment of rent. Additionally, Wisconsin recognizes the implied duty of good faith and fair dealing in contracts, which means that landlords are expected to exercise fairness in their dealings with tenants, including the imposition of late fees. If a lease specifies a particular time by which rent is due and emphasizes that timing is critical, a landlord may be justified in charging a late fee for rent paid past that time. However, charging a late fee for rent that is only an hour late without such a specific provision in the lease could potentially be seen as a breach of the duty of good faith and fair dealing. Tenants should read their lease agreements carefully to understand their obligations and the conditions under which late fees may be incurred.