Coast FIRE Calculator

The Coast FIRE calculation is a three-step process that works backward from your retirement spending needs to determine how much you need today:

Step 1: Calculate your FIRE number

FIRE Number = Annual Retirement Expenses / Safe Withdrawal Rate

If you plan to spend $50,000 per year in retirement and use a 4% safe withdrawal rate, your FIRE number is $50,000 / 0.04 = $1,250,000. This is the total portfolio value you need on the day you retire.

Step 2: Calculate your real (inflation-adjusted) return

Real Return = ((1 + Nominal Return) / (1 + Inflation)) − 1

If you expect 7% nominal returns and 3% inflation, your real return is ((1.07) / (1.03)) − 1 = 3.88%. This is the Fisher equation, which is more accurate than simply subtracting inflation from returns.

Step 3: Discount the FIRE number back to today

Coast FIRE Number = FIRE Number / (1 + Real Return)^Years Until Retirement

If your FIRE number is $1,250,000, your real return is 3.88%, and you have 30 years until retirement: Coast FIRE = $1,250,000 / (1.0388)^30 = about $397,000.

Key insight: The earlier you are, the lower your Coast FIRE number, because you have more years of compounding ahead. A 25-year-old has a much lower Coast FIRE number than a 45-year-old, even if they have the same FIRE number.

The 4% rule (also called the Trinity Study rule) states that if you withdraw 4% of your portfolio in the first year of retirement, then adjust that dollar amount for inflation each subsequent year, your portfolio has a high probability of lasting at least 30 years.

Where it comes from: The rule originated from a 1998 paper by three Trinity University professors who back-tested withdrawal strategies against historical U.S. stock and bond returns. Financial planner William Bengen had published similar findings in 1994. Both analyses found that a 4% initial withdrawal rate survived nearly all 30-year retirement periods in U.S. market history.

How it works in practice:

• Year 1: You have $1,000,000. You withdraw 4%, or $40,000.
• Year 2: Inflation was 3%. You withdraw $40,000 × 1.03 = $41,200 (regardless of portfolio performance).
• Year 3: Inflation was 2.5%. You withdraw $41,200 × 1.025 = $42,230. And so on.

Important caveats:

• 30-year horizon only — The original research tested 30-year periods. If you retire at 35 and live to 95, that's 60 years. A lower withdrawal rate (3-3.5%) may be more appropriate for early retirees.
• U.S.-centric data — The back-tests used U.S. market returns, which have been historically strong. Global returns have been lower on average.
• Not a guarantee — The 4% rule survived most historical periods, but not all. A severe bear market in your first few years of retirement (sequence of returns risk) can deplete the portfolio faster than the rule predicts.
• Assumes a balanced portfolio — The original research assumed a mix of stocks and bonds (typically 50/50 to 75/25). A 100% stock portfolio or 100% bond portfolio behaves differently.

For Coast FIRE planning, the 4% rule is used in reverse: your annual expenses divided by 4% gives you the total portfolio you need at retirement (your FIRE number). Many conservative planners use 3.5% or even 3% for longer retirement horizons.

Real (inflation-adjusted) returns are critical for any long-term financial planning because they tell you what your money can actually buy, not just how big the number on your account statement looks. When you're planning decades into the future, the difference is enormous.

The problem with nominal returns:

• If your portfolio grows at 7% nominally and inflation is 3%, your purchasing power only grows at about 3.88% per year (via the Fisher equation). Over 30 years, the nominal number will be roughly 2.4x larger than the real number.
• If you plan using nominal returns, you'll think your future portfolio will be much bigger than it really is in terms of what you can buy with it. This leads to under-saving.
• Your retirement expenses are quoted in today's dollars ($50,000/year means $50,000 of today's purchasing power). If you use nominal returns to project your portfolio but real dollars for expenses, the numbers don't match.

How this calculator handles it: We use the Fisher equation (Real Return = ((1 + Nominal) / (1 + Inflation)) − 1) to convert your expected nominal return into a real return. Then all projections are done in today's dollars. When we say your portfolio will be $500,000 at retirement, that means $500,000 of today's purchasing power — not some inflated future number that sounds impressive but buys less.

Why the Fisher equation? Simply subtracting inflation from the nominal return (7% − 3% = 4%) is a rough approximation. The Fisher equation gives the exact answer (3.88%) because it accounts for the compounding effect of inflation on your gains. The error grows larger over longer time horizons and with higher rates.

The FIRE movement has spawned several variations that reflect different lifestyles and risk tolerances. Understanding where Coast FIRE sits in the spectrum helps you pick the right target for your situation:

• Lean FIRE — Achieving financial independence with a very lean budget, typically under $40,000/year per person. Requires extreme frugality both before and after retirement. The FIRE number is smaller, but there's little margin for unexpected expenses.
• Regular FIRE — The standard goal: accumulate 25x your annual expenses (the inverse of the 4% rule) and retire. Typically targets $40,000-$80,000/year in expenses.
• Fat FIRE — Financial independence with a more generous lifestyle, typically $100,000+ per year in expenses. Requires a much larger portfolio (often $2.5M+) but provides a comfortable cushion for lifestyle inflation, travel, and unexpected costs.
• Barista FIRE — Similar to Coast FIRE but with a specific twist: you work a low-stress, often part-time job (the stereotype is a barista) primarily for health insurance and spending money, while your invested savings grow to your retirement number.
• Coast FIRE — You've saved enough that compounding will grow your portfolio to your FIRE number by retirement age without any additional contributions. You still work to cover current expenses, but you've removed the need to save for retirement.

Coast FIRE vs. Barista FIRE: These two are often confused. The difference is subtle but important. Coast FIRE is purely a mathematical milestone: you've reached the savings threshold where compounding handles the rest. Barista FIRE is a lifestyle choice: working a specific type of job (part-time, lower stress) after reaching or approaching financial independence. You can be at Coast FIRE and continue working your current career, or you can use Coast FIRE as the trigger to switch to a Barista FIRE lifestyle.

Which is right for you? Coast FIRE is the most accessible milestone for most people because it leverages time and compounding rather than requiring a massive portfolio. If you start saving in your 20s, you can realistically hit Coast FIRE in your 30s — decades before full FIRE.

Your assumptions for investment returns and inflation are the two most impactful inputs in the Coast FIRE calculation. Small changes compound dramatically over decades, so it's worth being thoughtful about these numbers.

Expected return guidelines:

• 7% nominal is a commonly used assumption for a diversified stock portfolio. The S&P 500 has returned roughly 10% nominally over the long run, but a diversified portfolio including bonds, international stocks, and other assets typically returns less.
• Conservative: 6% — Use this if you have a significant bond allocation, are concerned about lower future returns, or simply want a margin of safety.
• Aggressive: 8-9% — Use this only if you're nearly 100% in equities and willing to accept higher volatility. Not recommended for planning unless you have a very long time horizon.

Inflation guidelines:

• 3% (default) — Close to the long-term U.S. average (~3.0% since 1926) and a reasonable baseline for planning.
• 2-2.5% — The Fed's target rate. Use this if you believe central banks will succeed in keeping inflation low.
• 3.5-4% — A more conservative assumption if you think inflation will run above the Fed's target for structural reasons.

The real return is what matters: A 7% nominal return with 3% inflation gives you about a 3.88% real return. A 9% return with 5% inflation gives about 3.81% real. These feel very different but produce nearly identical Coast FIRE numbers. Focus on what real return you believe is sustainable, and work backward.

When in doubt: Use 7% nominal and 3% inflation (roughly 3.88% real). Then check the sensitivity table in the calculator to see how your Coast FIRE number changes at different retirement ages.

This is one of the most common concerns about Coast FIRE, and it's a legitimate one. Coast FIRE is a point-in-time calculation — it assumes your portfolio grows at the expected real return every year for the rest of the journey. Markets, of course, don't move in straight lines.

The good news:

• You have time on your side — Coast FIRE only applies when you have years (often decades) until retirement. Market downturns that happen early in that period are actually beneficial if you're still earning and reinvesting dividends, because you're buying more shares at lower prices.
• Historical recovery — The longest recovery time for a diversified U.S. stock portfolio from peak to peak has been about 13 years (after the 1929 crash). If you have 20-30 years, even a severe crash gives you plenty of recovery runway.
• The math self-corrects — If markets drop 30% after you hit Coast FIRE, you're temporarily below your Coast FIRE number. But the same market drop means future expected returns are likely higher (lower valuations = higher forward returns), which partially offsets the loss.

The risk to manage:

• Sequence of returns near retirement — If a major crash happens 2-3 years before your retirement date, you may not have enough time to recover. This is why most financial planners recommend shifting to a more conservative allocation (more bonds) as you approach retirement.
• Prolonged low returns — A lost decade (like Japan's 1990s or the U.S. 2000-2010) can severely impact your trajectory. This is a stronger argument for using conservative return assumptions (6% nominal instead of 8%) rather than worrying about individual crashes.

Practical advice: Even after hitting Coast FIRE, continuing to save even a small amount provides a margin of safety. You don't need to save as aggressively, but $200-500/month as a buffer can protect against worst-case scenarios.

Coast FIRE and DCF (Discounted Cash Flow) analysis might seem unrelated at first, but they share the same fundamental concept: the time value of money and the power of compounding.

The connection:

• Coast FIRE discounts backward: You take a future number (your FIRE number at retirement) and discount it back to today using your expected real return. This is exactly what a DCF model does — it takes future cash flows and discounts them back to today's value using a discount rate (WACC).
• Both are sensitivity-driven: Small changes in the discount rate or growth assumptions dramatically change the output. A 1% change in your expected return shifts your Coast FIRE number by tens of thousands of dollars, just like a 1% change in WACC can swing a stock's fair value by 20-30%.
• Both rely on the same return assumptions:Your Coast FIRE projection assumes your portfolio grows at a certain real rate. But what drives that growth? The individual stocks, bonds, and funds in your portfolio. A DCF model helps you evaluate whether individual investments are likely to deliver the returns your Coast FIRE plan depends on.

How to use both together:

• Use the Coast FIRE calculator to determine your target and the real return you need.
• Use DCF analysis to find individual stocks trading below their intrinsic value, which are more likely to deliver the returns your plan requires.
• If your DCF models suggest your portfolio stocks are overvalued, that's a signal to reassess your Coast FIRE timeline or adjust your savings rate.

Bottom line: Coast FIRE tells you the destination. DCF analysis helps you pick the vehicle.

Yes, and it's more realistic than most people think. The magic of Coast FIRE is that the earlier you start, the less you need to save, because compounding has more years to work. A 25-year-old targeting retirement at 65 has 40 years of compounding — an incredibly powerful force.

Some example Coast FIRE numbers (assuming 7% nominal return, 3% inflation, 4% SWR, and $50,000/year retirement spending):

• Age 25 (40 years to 65): Coast FIRE number is approximately $274,000. Save this by 25 and you never need to save for retirement again.
• Age 30 (35 years to 65): Approximately $328,000.
• Age 35 (30 years to 65): Approximately $397,000.
• Age 40 (25 years to 65): Approximately $479,000.

How to get there faster:

• Start early — Even small amounts in your early 20s have decades to compound. $500/month from age 22 to 30 (8 years) at a 7% nominal return gives you roughly $60,000 — which becomes a meaningful chunk of your Coast FIRE number.
• Maximize tax-advantaged accounts first— 401(k) matches, Roth IRA contributions, and HSA investments all grow tax-free or tax-deferred, making your real return effectively higher.
• Increase income, then savings rate — Focus on earning more (career moves, skills, side income) and routing the increase to investments before lifestyle inflation takes hold.
• Use windfalls wisely — Bonuses, tax refunds, and gifts can make outsized contributions to your Coast FIRE number when invested early.

The liberating part: Once you hit Coast FIRE in your 30s, the pressure to earn a high income disappears. You can pursue creative work, start a business, travel, or take career risks that would be terrifying without the safety net of knowing your retirement is locked in.

Coast FIRE is a powerful framework, but like any financial model, it has assumptions that may not hold. Understanding the limitations helps you plan more robustly:

Key risks:

• Return assumptions may be wrong — The entire Coast FIRE concept depends on your portfolio growing at the expected real rate. If real returns average 2% instead of 4%, your Coast FIRE number is significantly higher than calculated. Always check the sensitivity table at different retirement ages.
• Inflation may exceed expectations — High inflation erodes real returns. A decade of 5-6% inflation with only 7% nominal returns leaves you with just 1-2% real growth — far less than the typical 3.88% used in Coast FIRE math.
• Expenses change over time — Your $50,000/year estimate for retirement spending may be wrong. Healthcare costs tend to increase faster than general inflation. Lifestyle creep, family needs, and unexpected expenses can push your actual spending significantly higher.
• The SWR may not hold — The 4% rule was based on historical U.S. data. Future returns may be lower (higher current valuations imply lower forward returns), which could mean 3-3.5% is a safer withdrawal rate. This directly increases your FIRE number and therefore your Coast FIRE number.
• Behavioral risk — Once you hit Coast FIRE, the temptation to dip into savings or make poor investment decisions increases because the money feels less urgent. Staying invested through downturns is harder when you're no longer actively contributing.
• Life happens — Divorce, disability, job loss, family emergencies, or other major life events can force you to tap retirement savings, resetting your Coast FIRE status.

How to mitigate: Build in a margin of safety. Use conservative return assumptions (6% nominal instead of 8%), pad your expense estimate by 20%, and continue saving even a small amount after hitting Coast FIRE. The goal is robustness, not precision — your future self will thank you for the buffer.