A version of FIRE where someone retires early on a smaller portfolio, supporting a deliberately minimal, low-cost lifestyle — often defined as annual spending under roughly $40,000.
Think of it as the express lane to early retirement: you need less money to get there because you plan to spend less once you arrive. No big house, no frequent travel splurges — just the essentials, done comfortably but simply. It's not about deprivation for its own sake; it's a trade-off some people happily make in exchange for freedom sooner.
Someone living on $35,000/year needs roughly $875,000 invested (25× expenses) — versus $2M+ for someone spending $80,000/year. Lean FIRE gets you to the finish line faster, but leaves less cushion for surprise expenses or lifestyle upgrades later.