Coast FIRE Number
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Planning estimate
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CoastFI Calculator
Estimate how much you need invested today to coast to retirement.
CoastFI Inputs
The Ultimate Coast FIRE Calculator: Financial Independence on Easy Mode
The traditional FIRE movement (Financial Independence, Retire Early) demands extreme frugality. It often requires saving 50% to 70% of your income for a decade so you can quit the corporate grind in your 30s or 40s. While effective, this aggressive path leads to immense burnout and forces you to sacrifice the best years of your life to hyper-saving.
Coast FIRE is the psychological and financial antidote. You reach "Coast FIRE" the exact moment your current retirement and investment accounts are large enough that, without ever adding another single dollar, they will mathematically compound to reach your final retirement goal by your target age. Once you hit this magical number, you no longer need to save for the future. You can step down to a lower-stress job, work part-time, or simply spend 100% of your current paycheck guilt-free, knowing your traditional retirement is already fully funded by the sheer power of compound interest.
The Math Behind the Magic: How Coast FIRE Works
Calculating your Coast number requires reverse-engineering your traditional retirement goal using the time value of money.
Step 1: Your Target Nest Egg
First, determine how much money you need to retire comfortably. The industry standard is the "4% Rule," which states you can safely withdraw 4% of your portfolio every year indefinitely.
Target Nest Egg = Annual Spend ÷ 0.04
Step 2: The Coast Formula
Next, we calculate how much money you need today so that it grows into your Target Nest Egg without any future contributions.
Coast = Nest Egg ÷ (1 + Rate of Return)^Years
Real-World Use Case: The Power of Starting Early
Why is Coast FIRE so popular with younger generations? Because time is the ultimate multiplier in the compound interest formula. Let's compare two individuals who both want to retire at age 65 with a $1.5 Million portfolio (assuming an inflation-adjusted 7% return).
Sarah (Age 25)
- Years to Grow: 40 Years
- The Math: $1.5M ÷ (1.07)^40
- Coast FIRE Number: $100,161
If Sarah grinds hard and saves $100k by her 25th birthday, she is completely done saving for retirement. She can spend every penny she makes for the next 40 years.
John (Age 45)
- Years to Grow: 20 Years
- The Math: $1.5M ÷ (1.07)^20
- Coast FIRE Number: $387,626
Because John waited, his money has half the time to compound. His Coast FIRE number is nearly four times higher than Sarah's for the exact same retirement goal.
Frequently Asked Questions
What rate of return should I use?
Historically, the S&P 500 returns about 10% per year. However, inflation decreases your purchasing power by an average of 3% per year. To ensure your "Target Nest Egg" actually feels like a million dollars in the future, you should use an "inflation-adjusted" rate of return. The industry standard is 7%. If you want to be extremely conservative, use 5% or 6%.
What is Barista FIRE?
Barista FIRE is what many people choose to do immediately after reaching Coast FIRE. Once your traditional retirement is mathematically guaranteed, you quit your high-stress corporate job and take a low-stress, part-time job (like working at a coffee shop) just to cover your daily living expenses and get subsidized health insurance.
Should I really stop saving once I hit my Coast number?
You can, but most financial advisors recommend a "buffer." The stock market does not go up by exactly 7% every year; it is highly volatile. Hitting your Coast number means you have the mathematical freedom to scale back, but continuing to contribute small amounts acts as an insurance policy against poor market performance (Sequence of Returns risk).
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