What this tool does
The Coast FIRE Calculator determines the minimum amount of money you need to have invested right now so that, even if you never save another dollar, compound growth will grow your portfolio to your full Financial Independence (FI) number by retirement age. "Coast FIRE" means you have already saved enough to coast — you still work to cover current living expenses, but you no longer need to actively save for retirement. This concept is sometimes called "Coast FI" or "Barista FIRE" because once you reach the threshold, you could theoretically take a lower-paying or less stressful job (like a barista) and still retire comfortably. The calculator takes your current age, target retirement age, current savings balance, expected annual expenses in retirement, anticipated investment return rate, inflation rate, and safe withdrawal rate to produce your Coast FIRE number and show whether your current savings already meet or exceed that target. It also projects how your portfolio will grow over time with and without ongoing contributions, so you can visualize the power of compound interest working on your behalf.
How it calculates
The calculation proceeds in three steps. First, the tool computes your FI Number — the total portfolio you will need at retirement to sustain your desired lifestyle. It does this by inflating your annual retirement expenses to future (nominal) dollars using the formula: Inflated Expenses = Annual Expenses x (1 + inflation)^years. Then it divides by the safe withdrawal rate: FI Number = Inflated Expenses / SWR. Second, the tool discounts that future FI Number back to today using the expected nominal return: Coast FIRE Number = FI Number / (1 + return)^years. This tells you how much you need invested right now so that compound growth alone reaches the FI Number. Third, the tool compares your current savings to the Coast FIRE Number. If your savings meet or exceed it, you have reached Coast FIRE. The real (inflation-adjusted) return is calculated using the Fisher equation: Real Return = (1 + Nominal Return) / (1 + Inflation) - 1. Projection charts use the nominal return to show year-by-year portfolio growth, both with zero future contributions and with an illustrative \$500 per month in ongoing contributions.
Who should use this
This tool is ideal for anyone exploring the FIRE movement who wants a less aggressive path than traditional FIRE. It is especially useful for workers in their twenties and thirties who have been saving aggressively and want to know when they can ease off contributions. Freelancers and gig workers considering a shift to part-time or lower-income work will find it helpful for determining whether their existing nest egg is sufficient. Parents returning to the workforce after time away can use it to gauge whether past savings have compounded enough. Financial planners can use the tool to illustrate the power of early saving to clients. Anyone feeling burned out from a high-savings-rate lifestyle can benefit from seeing a concrete number that means "you can relax now."
Worked examples
Example 1: A 30-year-old with \$150,000 saved wants to retire at 65 on \$50,000 per year (today's dollars). They assume a 7% nominal return, 3% inflation, and a 4% safe withdrawal rate. Inflated annual expenses at 65: \$50,000 x (1.03)^35 = \$140,676. FI Number: \$140,676 / 0.04 = \$3,516,891. Coast FIRE Number: \$3,516,891 / (1.07)^35 = \$3,516,891 / 10.677 = \$329,399. Since \$150,000 is less than \$329,399, this person has not yet reached Coast FIRE and needs approximately \$179,399 more. Their current savings would grow to roughly \$150,000 x (1.07)^35 = \$1,600,612 by age 65 without further contributions — well short of the \$3.52 million FI Number.
Example 2: A 35-year-old with \$400,000 saved targets retirement at 60 on \$40,000 per year. Same 7% return, 3% inflation, 4% SWR. Inflated expenses: \$40,000 x (1.03)^25 = \$83,756. FI Number: \$83,756 / 0.04 = \$2,093,898. Coast FIRE Number: \$2,093,898 / (1.07)^25 = \$2,093,898 / 5.427 = \$385,815. With \$400,000, this person has surpassed Coast FIRE by about \$14,185. They can stop contributing to retirement accounts entirely and still expect their portfolio to reach roughly \$2.17 million by age 60, exceeding the required \$2.09 million.
Limitations
The calculator assumes a constant annual rate of return, which does not reflect real-world market volatility. Sequence-of-returns risk — the possibility of poor returns in the early years — is not modeled, yet it can significantly affect outcomes. Inflation is treated as a fixed rate, but actual inflation fluctuates and can spike unexpectedly. The safe withdrawal rate is a guideline derived from historical backtesting (the Trinity Study), not a guarantee. Healthcare costs, Social Security income, pensions, and taxes are not factored in, all of which can materially impact retirement readiness. The projection charts show a smooth growth curve that will differ from the jagged path of real market returns. Additionally, the \$500/month contribution scenario is illustrative only and may not match your actual savings plan. This tool is for educational planning purposes and should not replace personalized advice from a qualified financial advisor.
FAQs
Q: What is the difference between Coast FIRE and regular FIRE? A: Regular FIRE is the total amount you need to retire and live off your portfolio indefinitely. Coast FIRE is the smaller amount you need saved today so that compound growth alone will reach that regular FIRE number by retirement age. Once you reach Coast FIRE, you only need to earn enough to cover current expenses — retirement saving becomes optional.
Q: Does Coast FIRE mean I can stop working entirely? A: No. Coast FIRE means you can stop saving for retirement, but you still need income to cover your day-to-day living expenses until you actually retire. Many people who reach Coast FIRE choose to switch to less demanding or lower-paying work, since they no longer need to maximize savings.
Q: How does the safe withdrawal rate affect my Coast FIRE number? A: A lower safe withdrawal rate means you need a larger portfolio at retirement (higher FI Number), which in turn raises the Coast FIRE number. For example, using a 3.5% SWR instead of 4% increases the FI Number by about 14%, and the Coast FIRE Number rises proportionally. More conservative withdrawal rates provide a greater safety margin but require more savings.
Q: What return rate should I use? A: A commonly used figure is 7% nominal (roughly 10% average stock market return minus 3% inflation), but this depends on your asset allocation. A portfolio with more bonds will have a lower expected return. If you want to be conservative, use 5-6%. The calculator lets you adjust this value so you can see how different assumptions affect your Coast FIRE number.
Q: Can I reach Coast FIRE earlier by reducing my expected retirement expenses? A: Yes. Lower expected expenses reduce both the FI Number and the Coast FIRE Number. For example, cutting planned retirement spending from \$50,000 to \$40,000 per year reduces the Coast FIRE Number by 20%. This is one of the most powerful levers available, since it lowers the target at every stage of the calculation.
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