Lean FIRE on $750K vs Fat FIRE on $2.25M vs Coast FIRE by 40 Are Three Different Lives, Not Three Points on One Curve
Most FIRE (Financial Independence, Retire Early) calculators answer one question: what’s my portfolio target? That’s a useful number, but it assumes the harder question — which version of financial independence am I actually optimizing for — has already been answered. It usually hasn’t.
Six paths, one underlying formula
Portfolio target = target annual spending × 25 (the inverse of the Trinity Study’s 4% safe withdrawal rate)
| Path | Target annual spending assumption |
|---|---|
| Lean FIRE | Fixed minimal target (e.g., $30K) |
| Regular FIRE | Current spending |
| Fat FIRE | ~1.5× current spending |
| Coast FIRE | Same as Regular, but you stop contributing once on track |
| Barista FIRE | ~50% of current spending (part-time work covers the rest) |
| Geo-Arbitrage FIRE | ~55% of current spending (via relocation) |
All six paths share the identical underlying math — the 25x multiplier on target spending — and differ only in what each path assumes “target annual spending” actually is. This is why comparing them side by side, from the same starting income and savings inputs, is more useful than calculating any single path in isolation: the six numbers reveal genuinely different portfolios and genuinely different lifestyles, not six versions of the same plan.
Why Coast FIRE is a special case
Unlike the other five paths, Coast FIRE isn’t defined by a spending target — it’s defined by a specific age. The calculation iterates forward from the present to find the earliest age at which current savings, left completely alone to compound with zero further contributions, would still reach the full Regular FIRE number by the target retirement age. Reaching that age with an adequate balance means, in theory, contributions can stop entirely and compound growth alone carries the portfolio the rest of the way — though in practice, most people pursuing Coast FIRE continue working and spending during the “coast” period, simply without the pressure of continued aggressive saving.
Why the sourced assumptions matter
The 4% withdrawal rate underlying the 25x multiplier traces back to the Trinity Study (Cooley, Hubbard, and Walz, 1998) and the related earlier work by Bengen (1994) that established the original “SAFEMAX” sustainable withdrawal rate research. The real-return assumption used to project years-to-reach each target draws on Robert Shiller’s long-run historical dataset, commonly cited in the 6.5-7% real US stock return range. The specific Lean/Coast/Barista naming taxonomy itself comes from the FIRE community’s own writing, notably ChooseFI and Mr. Money Mustache’s blogs — these aren’t academic terms, but they’ve become the standard vocabulary for describing these distinct paths.
Why seeing all six matters more than picking “the right one”
The tool’s real value isn’t identifying a single correct path — it’s putting six genuinely different portfolio targets and genuinely different lifestyles on the same screen, calculated from the same starting inputs, so the comparison itself becomes informative. Someone might discover their Coast FIRE age is much closer than expected, or that Barista FIRE requires a dramatically smaller portfolio than Fat FIRE for a lifestyle that’s still genuinely comfortable — insights that don’t surface from calculating any single path’s number in isolation.
Where this framework doesn’t apply
- A single real-return assumption doesn’t capture market variability. This tool uses one flat assumed return per calculation; a full Monte Carlo simulation (as used in the separate FIRE Calculator) models a distribution of possible outcomes rather than one deterministic path.
- Social Security and pensions aren’t modeled here. Any expected future Social Security or pension income would reduce the required portfolio target dollar-for-dollar against spending needs — a meaningful omission for anyone with a substantial expected benefit.
- Taxes during accumulation aren’t explicitly modeled. The real-return assumption implicitly folds in some tax drag, but doesn’t explicitly model account-type-specific tax treatment during the saving years.
- Barista FIRE’s healthcare cost assumption is a simplification. The model assumes part-time work income covers healthcare costs for the Barista FIRE path — a real but unmodeled variable, since healthcare access and cost through part-time employment varies enormously.
What to actually do
- Run all six paths with your actual income and savings inputs before assuming any single FIRE variant is “the” goal.
- Pay particular attention to your Coast FIRE age — it’s often a more actionable, nearer-term milestone than a full FIRE number.
- Treat the 25x/4% withdrawal rate as a well-researched planning baseline, not a guarantee — the underlying research describes historical success rates, not certainties.
- Layer in your own expected Social Security or pension income manually, since the comparator doesn’t include it, to avoid overestimating your required portfolio.
- For a full probability-based projection rather than a single deterministic estimate per path, follow up with the site’s separate Monte Carlo FIRE Calculator.
Open the FIRE Path Comparator → and see all six paths calculated from your own income and savings.