Coast FIRE: the math of stopping early
6-minute read · Updated August 2026 · Pairs with the Coast FIRE Calculator
The short answer
Coast FIRE is the point where your portfolio can finish the job without another contribution: invested money compounds toward your retirement target while you only earn enough to cover today. The math: retirement target ÷ (1 + real return)years to retirement. A $900,000 target, 30 years out at a 5% real return, is “coasted” from about $208,000 today.
How is Coast FIRE different from regular FIRE?
Regular FIRE asks: when can I stop working entirely? That needs the full target — annual spending × 25 under the 4% rule. Coast FIRE asks a smaller, earlier question: when can I stop saving? Because compounding does more of the work the more years it gets, the Coast threshold arrives decades before the full number — and reaching it changes what your paycheck has to do.
What does coasting look like at different ages?
| Age today | Years to 60 | Growth factor at 5% real | Coast number for a $900k target |
|---|---|---|---|
| 30 | 30 | ×4.32 | ≈ $208,000 |
| 35 | 25 | ×3.39 | ≈ $266,000 |
| 40 | 20 | ×2.65 | ≈ $339,000 |
| 45 | 15 | ×2.08 | ≈ $433,000 |
Growth factor = 1.05^years. Real (after-inflation) return, so the target stays in today's money. Figures rounded.
Read the table backwards and it's a compounding lesson: the 30-year-old needs less than half the 45-year-old's portfolio for the same retirement, purely because their money gets 15 more years of growth. Early contributions aren't just savings — they're time leverage.
What's the catch?
Coasting is a bet on your return assumption holding for decades, with no contributions left to correct a bad stretch. Sensible guardrails: assume real (after-inflation) returns, not nominal; re-check the math yearly; and treat Coast status as permission to downshift, not an obligation to stop saving — many people keep contributing anyway and simply enjoy that they no longer have to.
Frequently asked questions
What is Coast FIRE in one sentence?
Coast FIRE is the point where your existing portfolio, left alone to compound, will reach your retirement target by retirement age — so you only need to earn enough to cover today's living costs.
How do I calculate my Coast FIRE number?
Divide your retirement target by growth until retirement: target ÷ (1 + real return)^years. Example: a $900,000 target, 30 years out, at a 5% real return needs $900,000 ÷ 4.32 ≈ $208,000 invested today.
Does Coast FIRE mean I stop working?
No — that's the point. You keep working to pay for today, but you stop needing to save for retirement. That freedom often funds a career change, part-time work, or a lower-stress job.
What return should I assume for coasting?
Use a real (after-inflation) return so your target stays in today's money — 4–5% real is a common planning range for a diversified portfolio. Higher assumptions shrink the Coast number but raise the risk it doesn't materialize.