The Coast FIRE Checkpoint — When You Can Stop Saving

Coast FIRE is the moment you can stop adding money to retirement and still retire on time. For most U.S. earners with a moderate savings habit, it arrives around age 35 — far earlier than people expect.

FIRE the movement has spawned a small zoo of related acronyms — Lean FIRE, Fat FIRE, Barista FIRE, Coast FIRE — and Coast is the most useful of them, because it's the only one that describes a checkpoint you can cross long before retirement. The other variants describe destinations. Coast describes a turning point. The math is simple, the implication is large, and most people who would benefit from knowing they're past it haven't run the calculation.

The definitions, briefly

FIRE means your invested portfolio is large enough to support your annual spending indefinitely — typically 25× annual spending using the 4% Rule. Lean FIRE is the same milestone reached on a low spending level (around $30,000/year); Fat FIRE is the same milestone on a high spending level (above $100,000/year). Coast FIRE is different: it's the portfolio size today that will grow into your full FIRE number by your target retirement age, at your assumed return, with no further contributions. Past it, your retirement is on autopilot — you only need earned income for current spending, not for future saving.

Coast_FI = (annual_spending × 25) ÷ (1 + r)^n

The threshold falls fast with time

The Coast threshold is sensitive to your time horizon in a way that rewards starting early aggressively. A 25-year-old aiming to retire at 65 has forty years for the portfolio to compound, and at 7% real their Coast threshold is roughly one-fifteenth of their FIRE number — meaning a $70,000 portfolio today will grow into a $1,000,000 retirement. The same person at 35 needs $190,000 to coast; at 45, $510,000. Every decade of delay roughly triples the Coast threshold. The sandbox to the right makes this concrete against your specific numbers.

What "winning" actually means

Being past Coast doesn't mean you can retire. You still need earned income to cover current living expenses, since your invested portfolio is reserved for the future. What changes is that the savings pressure evaporates. Your retirement is going to happen whether you keep saving or not. That opens a different set of career and life options that are typically unavailable to someone still trying to feed the portfolio.

Three common moves: downshift — take a lower-paying but higher-quality job that wouldn't have supported your previous savings rate but easily supports current expenses; gap year — actually unplug, knowing the accumulation continues without you; launch a business — the riskiest career move you'll never make becomes affordable when your retirement isn't betting on it.

The hidden caveats

Coast FI assumes a constant real return. Real returns aren't constant — they arrive in clusters, and a lost decade right after you cross Coast can push you back below it for years. The sandbox on this page reports one number against one return assumption; the full simulator handles variable returns via Monte Carlo and reports the probability your Coast holds.

Three more honest caveats. ACA pre-65. If your "downshift" loses you employer health insurance, the marketplace cost can be several thousand a year, eroding your current cash flow. Inflation surprises. Coast assumes you nail future spending in today's dollars; a sustained 4–5% inflation regime makes the target a moving one. Career re-entry risk. If you downshift and then need to ramp back up, the gap on the résumé matters in some fields more than others.

What to do today

1. Run the number against your real portfolio. Plug your invested assets (not net worth — invested) into the sandbox. Use both 5% and 7% return assumptions. If your portfolio is above the 5% line, you're conservatively past Coast. Between the two, you're past on standard assumptions but vulnerable to a lost decade.

2. If past, recalibrate. The standard advice for Coasters is to direct future savings to basis step-ups, Roth conversion seed money, or simply to current life. Continuing to max retirement when you've crossed Coast is often suboptimal — the marginal dollar buys you less than it would buy spent today.

3. If close, set a target year. Coast moves toward you as you age — every year shaves the Coast threshold. Set the year you expect to cross and run the model annually against your actual numbers.

Where to go from here

The Compounding Engine covers the math that gets you to Coast. The Drawdown Stress Test covers what happens after retirement — when Coast becomes actual FIRE. And the full simulator models all three milestones (Coast, Lean, Fat) under variable returns so you can see how your specific plan holds up.