Coast FIRE Calculator

What is Coast FIRE?

Coast FIRE (also called Coast FI) is the point where you've saved enough that compound growth alone will reach your full FIRE number by your target retirement age — no additional contributions needed.

Think of it as planting a tree. Once it's established and big enough, you don't need to keep watering it every day—it'll grow on its own. Your job shifts from aggressive accumulation to simply not touching what you've built.

The appeal is obvious: you can downshift to a less stressful, lower-paying job that just covers your current expenses. No more optimizing for income. No more grinding for promotions you don't want. You work to live, not to save.

The term emerged from online FIRE communities around 2018-2019 and was popularized by writers like Jessica at The Fioneers, who used her own Coast FI milestone to transition to part-time work. The r/coastFIRE subreddit (51,000+ members) remains the largest dedicated community.

For many people, especially those who discovered FIRE later in life or who don't have high incomes, Coast FIRE is a more achievable milestone than traditional FIRE. It's proof that financial independence isn't all-or-nothing—there are meaningful waypoints along the journey.

How Coast FIRE Works

The math behind Coast FIRE is the inverse of compound growth. Instead of asking "how much will this grow to?", you ask "how much do I need now to reach that target?"

The formula is straightforward:

Coast FI Number = FIRE Number ÷ (1 + return rate)^years

Let's say your FIRE number is $1,200,000 (based on $4,000/month expenses and the 4% rule). You're 30 years old and plan to fully retire at 65. That's 35 years of growth. Assuming 7% real returns — the historical average for U.S. stocks after inflation, confirmed independently by Damodaran's NYU dataset (6.9%, 1928–2024) and Shiller's Yale dataset (7.1%, 1871–2024):

Coast FI = $1,200,000 ÷ (1.07)³⁵ = $1,200,000 ÷ 10.68 = $112,360

If you have $112,360 invested at age 30 and never add another dollar, you'll have $1,200,000 by 65 (in today's purchasing power, since we used real returns).

The Variables That Matter

The power of time is dramatic. At 25 with 40 years to retirement, you might only need $80,000 to coast. At 45 with 20 years left, you'd need $310,000 for the same retirement lifestyle. Starting early matters enormously.

Coast FIRE vs Traditional FIRE

Traditional FIRE means accumulating your full retirement number as fast as possible—usually through aggressive saving of 50%+ of income—then stopping work entirely.

Coast FIRE is a waypoint, not the destination. You hit a smaller number earlier, then shift how you work rather than stopping work altogether.

Neither is inherently better. Traditional FIRE gets you to full freedom faster but requires more sacrifice. Coast FIRE lets you enjoy life sooner but means working (at least part-time) for longer. Many people end up somewhere in between. For a deeper comparison with another popular alternative, see Coast FIRE vs Barista FIRE.

The Risks of Coast FIRE

Coast FIRE depends on a return assumption over decades. That's the fundamental bet. Financial Samurai called it "the most dangerous early retirement strategy" for this reason — and while that framing is deliberately provocative, the underlying concern is legitimate.

Return Assumptions Can Be Wrong

The 7% real return figure is a long-run average. But returns over any specific 30-40 year period have varied significantly. Someone who started investing in 1929 experienced different outcomes than someone who started in 1982. The historical range for 35-year real returns on U.S. stocks spans roughly 5% to 9% annualized — and that spread changes your Coast FI number dramatically.

No Dollar-Cost Averaging Safety Net

When you stop contributing and coast, you lose the benefit of buying shares at lower prices during downturns. A traditional saver buying through a crash benefits from dollar-cost averaging. A coaster just watches their portfolio drop and hopes it recovers in time. Research by Frank and Blanchett found that investors with identical average returns can see terminal values differ by 25% due to the sequence those returns arrive in.

Expenses Change More Than You Think

The biggest critique: your expenses at 30 may bear little resemblance to your expenses at 50. Kids, healthcare costs, aging parents, housing changes — life has a way of inflating your spending. The Bureau of Labor Statistics shows healthcare is the fastest-growing expense category for American households.

Mitigating the Risk

None of this means Coast FIRE is a bad strategy. It means it requires honest assumptions and a buffer:

• Use conservative returns (5-6% real instead of 7%) and treat any outperformance as a bonus
• Build a 10-20% buffer above your Coast FI number before you stop contributing
• Keep some savings capacity — even $200/month into a brokerage account keeps the muscle active
• Revisit yearly — if your portfolio is tracking below the growth curve, you can adjust

How does your Coast FIRE number hold up across different market conditions? Fire Planner runs Monte Carlo simulations across 1,000+ randomized return sequences and backtests your plan against every historical period since 1871 — including the scenarios where coasting through a crash erases your margin.

For a deeper analysis of what actually happens when people start coasting — including the job, identity, and lifestyle challenges — see The Coast FIRE Myth.

Who is Coast FIRE For?

Coast FIRE makes the most sense if you:

• Started saving young: A 25-year-old with $50,000 invested is already close to Coast FI for many retirement targets. Time is your superpower.
• Want to change careers: Hate your high-paying corporate job? Coast FI gives you permission to become a teacher, artist, or barista without sacrificing retirement security.
• Value present enjoyment: Some people don't want to defer all happiness until retirement. Coast FI lets you optimize for life satisfaction now.
• Have variable income: Freelancers, entrepreneurs, and gig workers can aggressively save during good years, hit Coast FI, then ride out lean years without stress.
• Found FIRE late: If you're 40 with modest savings, traditional FIRE might feel impossible. Coast FI is a more realistic goal that still changes everything.
• Living outside the US: The FIRE math is universal. Compound growth works the same in any currency. Use the currency selector to plan in EUR, GBP, JPY, CAD, AUD, CHF, or INR.

Coast FIRE Number by Age

Don't want to plug in numbers? Here's a quick reference. These assume retiring at 65 with a 7% real return and a 4% withdrawal rate — the same defaults the calculator uses above.

The pattern is clear: every five years you wait roughly doubles your Coast FI number. A 25-year-old needs $80,136 to cover $4,000/month expenses in retirement. A 50-year-old needs $434,935 for the same lifestyle. Starting early is the single biggest lever.

How sensitive are these numbers? The table above uses 7% real returns. At a more conservative 5%, the Coast FI numbers jump significantly — for example, the age 30 / $4,000-per-month figure rises from $112,396 to $217,548 (a 94% increase). The younger you are, the more sensitive your number is to the return assumption, because small rate differences compound over more years. This is why many planners recommend using 5-6% for Coast FIRE calculations and treating 7% as a best-case scenario.

After You Hit Coast FI

Reaching your Coast FI number doesn't mean you have to stop saving. But it means you can. Based on r/coastFIRE discussions, the most common paths fall into two categories:

Most People: Change the Mindset, Not the Job

The surprise finding from our analysis of Coast FIRE discussions: the majority of people who hit Coast FI don't quit or switch jobs. They redirect retirement contributions to travel, hobbies, and lifestyle upgrades. They set boundaries at work — "meets expectations" becomes a perfectly fine performance review. They use all their PTO, say no to extra projects, and stop optimizing for promotions. Same job, completely different relationship with it.

Some People: Actually Change the Work

For those who do make a move, the most effective paths are consulting or contracting in their existing field (higher hourly rate, fewer hours), going part-time at their current employer, or starting a business with the safety net of Coast FI removing the pressure to be profitable immediately. The mythical "easy coast job" — low stress, decent pay, good benefits — is much harder to find than expected.

The "One More Year" Trap

Warning: Coast FI can become an excuse to never make a change. "I'll just save a bit more to be safe" year after year defeats the purpose. If you've hit your number and built in a reasonable buffer, trust the math and make your move.

Coast FIRE is one of several FIRE strategies. Where it fits: Lean FIRE targets minimal spending, Traditional FIRE targets full financial independence, Barista FIRE adds part-time work, and Fat FIRE aims for a comfortable lifestyle. Coast FI sits between — more accessible than Traditional, more patient than Barista.