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 New York, a residential tenant's rights and a landlord's responsibilities are indeed most comprehensively detailed in the written lease agreement. New York law allows landlords to use oral agreements for residential leases that are for less than one year, but written leases are strongly recommended as they provide a clear record of the terms agreed upon by both parties. Tenants should read and understand the lease before signing, as it is a binding legal document. Regarding late fees, New York State law, specifically the Housing Stability and Tenant Protection Act of 2019, restricts landlords from charging late fees until rent is five days late and caps the fee at $50 or 5% of the monthly rent, whichever is less. Additionally, the implied covenant of good faith and fair dealing in New York contract law requires that both parties act honestly and fairly in the performance and enforcement of the lease, which means that a landlord may be acting in bad faith if they impose late fees in an unreasonable manner, such as charging for rent that is only an hour late without a specific provision in the lease stating that time is of the essence.