FIRE stands for financial independence, retire early, and the community around it has spawned enough variants to fill a menu. Coast, lean, fat, barista. They sound like different philosophies. They're really just different settings on the same calculation, and once you see the base sum, the whole taxonomy stops being confusing.
The base number: 25 times spending
Everything starts with the 4% rule, which says a diversified portfolio can historically support withdrawing 4% of its starting value each year, adjusted for inflation, without running dry over a long retirement. Flip 4% upside down and you get 25. So your FIRE number is 25 times your annual spending.
Spend $50,000 a year and the target is 25 times $50,000, which is $1,250,000. That's the whole formula. Notice what it depends on: your spending, not your income. Two people on identical salaries can have wildly different FIRE numbers, and the one who spends less wins twice, once because the target is smaller and again because they're saving more towards it.
Coast FIRE: let time do the lifting
Coast FIRE is my favourite of the variants because it's the one that changes how the journey feels. The idea: you don't need the full $1,250,000 today. You need enough invested today that compound growth alone gets you there by normal retirement age, with no further contributions.
Here's what that looks like. Take that $1,250,000 target. At age 30, with retirement at 65 and 6% real returns, the coast number is $162,632. Hit that by 30 and you can, in theory, never save another penny for retirement and still arrive at the full target at 65. The other 35 years of growth do the work.
You still have to earn enough to live on in the meantime, so it's not retirement. But it changes what your job has to be. Once you've coasted, work only needs to cover today's bills, not today's bills plus tomorrow's freedom. Our Coast FIRE calculator will find your own coast number from your age, target and return assumptions.
Lean FIRE: shrink the target
Lean FIRE attacks the other input. If the target is 25 times spending, then cutting spending cuts the target, hard. Engineer your life to run on $30,000 a year and the sum becomes 25 times $30,000, which is $750,000. That's $500,000 less than the $50,000 lifestyle needs.
The honest caveat: the maths only holds if the low spending is genuinely sustainable for decades. A budget you can white-knuckle for two years isn't a retirement plan. Lean FIRE works for people who actually like living lean, and quietly fails for people pretending to.
Fat FIRE: pay for comfort
Fat FIRE goes the other way. You want more comfort in retirement than your current spending suggests, so you set a bigger target and accept it takes longer to reach. There's no separate formula, it's still 25 times spending, just with a larger spending figure you've chosen on purpose. Nothing wrong with it. It's simply an admission that freedom and comfort both cost money and you're buying both.
Barista FIRE: cover the gap with part-time work
Barista FIRE sits between coasting and fully retiring. You quit the main career before the portfolio can support you completely, and part-time work covers the gap while the investments keep growing underneath. The name comes from the stereotype of pulling espresso shots for the health insurance, but the structure is general: a small income takes pressure off the portfolio during its best growing years.
It pairs naturally with Coast FIRE. If you've already hit your coast number, the part-time job only needs to cover living costs, and even a modest income can do that. The two ideas together are how a lot of people actually step down from full-time work in practice, rather than the clean cliff-edge retirement the headlines describe.
Picking a flavour
I'd stop worrying about which label fits and just run the numbers. Work out your annual spending, multiply by 25, and see where you stand against that target. Then try the variants: what happens if spending drops, if you coast from here, if part-time income covers half your costs. Our retirement calculator lets you play out those scenarios properly, with your own contributions and timeline, which beats arguing about definitions on a forum.
The variants are all the same idea wearing different hats. Spend less than you earn, invest the gap, and decide how much of the journey you want time, frugality or part-time work to carry for you.