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 Idaho, the primary source of information regarding tenant rights and landlord responsibilities is indeed the written lease agreement. Idaho law recognizes both written and oral lease agreements, but written leases provide clearer evidence of the terms agreed upon by the landlord and tenant. Tenants are encouraged to read and understand the lease before signing, as it is legally binding. Regarding late fees, Idaho's landlord-tenant laws do not specifically cap late fees; however, the fees must be reasonable and related to the actual costs incurred by the landlord due to the late payment. The lease agreement should clearly outline any late fee provisions, including the amount and when they are assessed. Under Idaho law, there is an implied covenant of good faith and fair dealing in contracts, which means that landlords must act fairly and may not impose late fees in an unreasonable or punitive manner. 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 specific terms in the lease could potentially be seen as a breach of the implied duty of good faith and fair dealing.