Coast FIRE Calculator

What is Coast FIRE?

Coast FIRE is a milestone on the way to full financial independence. You reach it the moment your invested portfolio becomes large enough to compound, on its own, into your full retirement target by the time you retire — even if you never add another dollar. From that point forward, you only need to earn enough to cover your current living expenses. Additional saving becomes optional.

It's a useful number because it changes how you think about your career. Most personal-finance advice assumes you save aggressively until you can retire entirely. Coast FIRE introduces a middle waypoint: a portfolio size that buys you flexibility long before traditional retirement. Once you're past it, you can downshift to a lower-paying job you actually enjoy, switch to part-time, take a sabbatical, or just stop worrying about whether you're saving enough.

The math

Coast FIRE rests on two ideas: the 4% rule for sustainable withdrawals, and compound growth for projecting today's portfolio to a future date.

Your FIRE number is the portfolio size that, withdrawn at a safe rate, covers your annual spending forever:

FIRE Number = Annual Expenses ÷ Safe Withdrawal Rate

At a 4% withdrawal rate, a household spending $40,000 per year needs a $1,000,000 portfolio. At 3.5%, the same spending needs ~$1,143,000.

Your Coast FIRE number is that future target, discounted backward at your expected real (after-inflation) return:

Coast FIRE Number = FIRE Number ÷ (1 + r)n

Where r is the annual real return (commonly 6–7%) and n is the number of years between today and your retirement age. A 30-year-old targeting retirement at 65 has 35 years of compounding ahead. At 7% real, that's a multiplier of ~10.7×: every dollar invested today becomes roughly $10.70 of retirement spending power.

A worked example

Say you're 32 years old, plan to retire at 65, and expect to spend about $50,000 per year (in today's dollars) once you stop working. You assume a 7% real return and use the 4% rule.

• FIRE number: $50,000 ÷ 0.04 = $1,250,000
• Years to retirement: 65 − 32 = 33 years
• Growth multiplier: 1.07³³ ≈ 9.33×
• Coast FIRE number: $1,250,000 ÷ 9.33 ≈ $134,000

That's the threshold. Once you have ~$134,000 invested, you can — in principle — stop saving and let compound growth carry you to $1.25M by 65. Anything you contribute beyond that simply pulls the date forward.

Coast FIRE doesn't force a decision — what changes is your relationship with your job.

How to use this calculator

1. Current age and retirement age set your compounding window. The longer the gap, the smaller your Coast FIRE number — time does most of the work.
2. Annual expenses in retirement is the lifestyle you're targeting, in today's dollars. Don't inflate it; the model handles inflation through the real-return input.
3. Current invested assets means your stocks, index funds, and retirement accounts. Exclude home equity, emergency cash, and anything you wouldn't draw on for retirement.
4. Real return is your expected post-inflation return. 7% is a common baseline for diversified equity. Lower it if you hold significant bonds or cash, or if you want a conservative buffer.
5. Withdrawal rate defaults to 4%. Lower it (e.g. 3.25–3.5%) if you're retiring very early or want a wider safety margin.

Coast FIRE vs Standard FIRE vs Lean FIRE

FIRE isn't one number — it's a family of milestones that differ in what lifestyle they fund and at what point you stop needing employment income.

• Standard FIRE: 25× annual expenses. Stop working today. The classic target.
• Lean FIRE: a smaller version of Standard FIRE based on minimal expenses ($25–40k/yr). Reachable earlier but tighter month-to-month.
• Barista FIRE: a portfolio plus part-time income that together cover expenses. Splits the gap between Coast FIRE and full retirement.
• Coast FIRE: the smallest of the four. You still need to earn your living expenses, but saving becomes optional.

Many people pursue them in sequence: hit Coast FIRE first (often in your thirties), keep working at a job you actually enjoy, then evaluate Barista or full FIRE in your forties or fifties.

What this calculator doesn't model

Coast FIRE math is intentionally simple. That's a feature — the math is easy to verify and the output is easy to reason about. But "simple" means the model leaves out real-world wrinkles:

• Sequence of returns risk. A single average return hides the difference between hitting a 30% drawdown at 35 vs 60.
• Tax drag. Returns inside taxable accounts get clipped by dividend and capital-gains taxes — fine to ignore as a first pass, but real money.
• Healthcare and retirement-specific expenses. US healthcare costs in particular tend to be back-loaded.
• Lifestyle creep. The model assumes today's spending translates to tomorrow's spending. In practice, expenses tend to grow faster than inflation as income grows.
• Social Security or other guaranteed income. If you expect a meaningful pension or social security check, your true Coast FIRE number is lower.

A common pragmatic adjustment is targeting 1.2–1.3× your Coast FIRE number, treating the buffer as insurance against any of the above going sideways.

What to do once you've reached Coast FIRE

The most under-appreciated thing about Coast FIRE is that it doesn't force a decision. You don't have to quit, downshift, or change anything the day you cross it. What changes is your relationship with your job: income from work goes from "necessary to retire on time" to "necessary only to cover your current life." Most people keep working — but the leverage shifts. You can negotiate harder, leave bad situations faster, and take more career risk.

A common pattern: hit Coast FIRE → keep saving aggressively for another few years to build a buffer → then either move to a job you love at lower pay, or push for full FIRE in your fifties.