TL;DR:No — there’s no legal 12‑month minimum; monthly, 6‑month and 12‑month leases are all common, though some owners or buildings may require 12 months.
No — Thai law does not require a 12‑month lease. Leases for residential property are flexible: you commonly find monthly, 3‑, 6‑ and 12‑month contracts. The legal trigger is duration: only leases longer than three years must be registered at the Land Department to be fully enforceable. Short‑term stays (monthly and multi‑month) are legal; daily/shorter-than-30‑day condo rentals face specific hotel‑licensing rules. Practically, some landlords or buildings set a 12‑month minimum for their own business reasons (management rules, mortgage or condominium regulations), so you will encounter annual-only listings in parts of Bangkok and high‑end developments. If you need certainty for a particular unit, ask the landlord/agency whether a shorter term is allowed and request the building’s rental/minimum term rules in writing. For legal detail see the Thai Land Department guidance and reputable legal firms such as Siam Legal on lease registration and short‑term rental rules.
Answer will be updated soon