The FHA does not set a legal expiration date for ESA letters. In practice, most housing providers look for documentation issued within the past 12 months, and a letter outside that window gives a landlord legitimate grounds to request updated paperwork before approving your accommodation request. For a state-by-state breakdown of ESA housing protections, see our ESA laws by state guide.
The real risk of letting your letter go stale is not immediate eviction. It is being caught without current documentation at the worst possible moment. That means a new application, a lease renewal, or a housing audit where your landlord decides to verify paperwork they previously accepted.
In practice, an ESA letter is valid for 12 months from the date it was issued. That date is printed on the letter itself. Once it passes, most landlords consider the letter outdated, regardless of whether your mental health need has changed.