Coast FIRE Calculator
A Coast FIRE calculator determines when you've saved enough that compound growth alone will fund your traditional retirement—without requiring any additional contributions. Coast FIRE represents a powerful milestone on the path to financial independence: the moment when time and compound interest will finish the job you started, allowing you to relax your savings rate and enjoy life more in the present.
Understanding Coast FIRE
Coast FIRE answers a simple but profound question: "How much do I need saved today so that, even if I never save another dollar, my investments will grow to my retirement number by age 65?" Once you reach this amount, compound growth does all the remaining work. You still need income to cover current living expenses, but every dollar you earn can be spent—retirement is mathematically guaranteed as long as you don't touch your investments.
Coast FIRE Formula
Coast FIRE Number = FIRE Number ÷ (1 + return)^years to retirement
This formula works backward from your retirement goal. If you need $1.5 million at age 65 and expect 7% real returns (after inflation), the formula tells you exactly how much you need today for compound growth to bridge the gap.
Coast FIRE Numbers by Age
Target: $1,500,000 at age 65, 7% real returns:
| Current Age | Years to 65 | Coast FIRE Number | Growth Multiple |
|---|---|---|---|
| 25 | 40 | $100,265 | 15.0x |
| 30 | 35 | $140,559 | 10.7x |
| 35 | 30 | $197,099 | 7.6x |
| 40 | 25 | $276,402 | 5.4x |
| 45 | 20 | $387,628 | 3.9x |
| 50 | 15 | $543,587 | 2.8x |
Coast FIRE Calculator Implementation
``javascript
function calculateCoastFIRE(targetFIRE, currentAge, retireAge, returnRate) {
const yearsToRetire = retireAge - currentAge;
const r = returnRate / 100;
// Present value of target FIRE number
const coastFIRE = targetFIRE / Math.pow(1 + r, yearsToRetire);
return {
coastFIRE: coastFIRE.toFixed(2),
yearsToRetire,
growthMultiple: Math.pow(1 + r, yearsToRetire).toFixed(2),
targetFIRE
};
}
console.log(calculateCoastFIRE(1500000, 35, 65, 7));
// { coastFIRE: '197099', yearsToRetire: 30, growthMultiple: '7.61' }
function checkIfCoasting(currentSavings, targetFIRE, currentAge, retireAge, returnRate) {
const coastNumber = calculateCoastFIRE(targetFIRE, currentAge, retireAge, returnRate);
const isCoasting = currentSavings >= parseFloat(coastNumber.coastFIRE);
return {
...coastNumber,
currentSavings,
isCoasting,
gap: (parseFloat(coastNumber.coastFIRE) - currentSavings).toFixed(2)
};
}
``
Life After Reaching Coast FIRE
Reaching Coast FIRE opens a world of possibilities. You can pursue passion projects without worrying about salary. Take a lower-paying but more fulfilling job. Start a risky business venture knowing retirement is secure. Work part-time and spend more time with family. Travel extensively while earning just enough to cover expenses. The psychological weight of "saving for retirement" lifts entirely—you've already done enough.
Coast FIRE vs Barista FIRE
Coast FIRE and Barista FIRE are often confused. Coast FIRE means compound growth will handle retirement—you work only to cover current expenses with no savings requirement. Barista FIRE means you've accumulated enough that part-time work (like being a barista) covers your living expenses while healthcare benefits bridge you to Medicare. Both represent partial financial independence milestones.
Conservative Coast FIRE Planning
Since Coast FIRE relies heavily on projected returns over long periods, consider building in a margin of safety. Using 5% returns instead of 7% is more conservative, as is targeting age 60 instead of 65. You can also continue saving small amounts after reaching Coast FIRE to hedge against sequence of returns risk or to reach full FIRE faster.