Coast Fire Calculator
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Reviewed for accuracy by Sahil, Senior Finance & Tax Editor
Coast Fire Calculator
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Formula: Coast FIRE Number = Annual Expenses x 25 / (1 + real return)^years | Real Return = Nominal - Inflation
Worked example — Already Coast FIRE! Savings will grow to $1.6M+
Formula
Coast FIRE Number = Annual Expenses x 25 / (1 + real return)^years | Real Return = Nominal - Inflation
Coast FIRE is when your current savings, growing at the expected return rate, will reach your FIRE number by retirement without additional contributions. FIRE number = 25x annual expenses (4% rule).
Worked Examples
Example 1: $150K at age 30
Problem:$150K savings, age 30, retire at 65, $50K/yr expenses, 7% return
Solution:FIRE number: $1.25M. Coast number: $1.25M/(1.07)^35 = $116,720. $150K > $116,720
Result:Already Coast FIRE! Savings will grow to $1.6M+
Frequently Asked Questions
What is Coast FIRE?
Coast FIRE means you have enough invested that, even without further contributions, compound growth will reach your full FIRE number by retirement. You still need to cover current expenses but can stop actively saving.
How is Coast FIRE different from Lean FIRE, Fat FIRE, and Barista FIRE?
These are all variations of the Financial Independence Retire Early (FIRE) movement with different portfolio and income requirements. Lean FIRE means fully retiring on a minimal budget (typically under $40,000 per year). Fat FIRE means fully retiring with a comfortable or luxurious budget (often $80,000 or more per year). Barista FIRE means semi-retiring and working part-time to cover current expenses while a smaller portfolio grows. Coast FIRE is a milestone status, not a retirement style — it means your current portfolio will reach your FIRE number by retirement age without additional contributions, though you still work to cover living costs.
Is a 7% real return assumption realistic for Coast FIRE calculations?
The historical real return (after inflation) of the US stock market has averaged approximately 7% per year over long periods based on S&P 500 data. However, this is not guaranteed and past returns do not predict future results. During any specific 20-35 year period, returns can be significantly higher or lower. Many financial planners use a more conservative 5-6% real return for long-range planning to provide a safety margin. The sequence-of-returns risk (getting poor returns early in your accumulation phase) also matters. Using a lower return assumption provides a buffer against underperformance.
What is Coast FIRE and how is it different from regular FIRE?
Coast FIRE is the point at which your current invested balance, left completely untouched with no further contributions, will grow through compounding alone to a full traditional-retirement-age nest egg. Unlike full FIRE, Coast FIRE does not mean you stop working entirely — it means you can stop saving for retirement specifically and cover only your current living expenses with active income, since your existing investments are already 'coasting' to the finish line on their own.
How does the math behind coasting actually work?
Coast FIRE works backward from your target retirement nest egg using the compound growth formula: required Coast FIRE balance = target nest egg ÷ (1 + assumed annual return)^(years remaining until retirement). The more years you have left before your target retirement age, the smaller the balance needed today, since compounding has longer to work — reaching Coast FIRE at 30 with 35 years to grow requires a much smaller number than reaching it at 45 with only 20 years left.
Does Coast FIRE mean I can stop working entirely?
No — Coast FIRE specifically means you can stop contributing to retirement accounts, not that you can stop earning income altogether. You still need active income (from a job, freelance work, or a lower-stress career switch) to cover current living expenses like housing, food, and healthcare, since the invested balance is earmarked to grow untouched until your target retirement date.
What rate of return assumption should I use for a Coast FIRE projection?
Most Coast FIRE projections use a long-run average real (after-inflation) equity return assumption, commonly in the 5-7% range, reflecting a diversified stock-heavy portfolio held over one or more decades. Using a lower, more conservative assumption produces a higher required Coast FIRE number and a more cautious plan; using an aggressive assumption produces a lower number but more risk if actual returns fall short.
How does reaching Coast FIRE early in your 20s or 30s change the required balance compared to reaching it at 40?
Because compound growth depends on time as an exponent, reaching Coast FIRE a decade earlier can cut the required balance dramatically — the same target retirement nest egg might require roughly half the invested balance at age 30 with 35 years to grow compared to age 40 with 25 years to grow, at the same assumed rate of return. This is why aggressive saving in your 20s and early 30s has an outsized effect on Coast FIRE timelines.
What happens to my Coast FIRE number if I plan to retire earlier than the standard retirement age?
Targeting an earlier retirement age shortens the number of years your current balance has to compound, which raises the required Coast FIRE number for the same target nest egg. It also means the coasting period itself (the years you're covering only living expenses without saving for retirement) is shorter, since your traditional retirement date arrives sooner.
Can market downturns push back my Coast FIRE date even if I've technically hit the number?
Yes. Coast FIRE calculations rely on an assumed average rate of return; a market downturn shortly after you 'coast' can leave your balance below the trajectory needed to reach your target nest egg on schedule. Some Coast FIRE planners build in a buffer above the bare-minimum coast number, or continue modest contributions during down markets, to protect against this timing risk.
Reviewed for accuracy by Sahil, Senior Finance & Tax Editor · Editorial policy
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