Coast FIRE is the point where your current investments, left alone, will grow into a fully funded retirement without another dollar saved. This free coast FIRE calculator finds that threshold from eight inputs: your age, target retirement age, invested assets, spending, withdrawal rate, expected return, inflation, and what you invest each month. It answers three questions at once: what your coast threshold is, whether you have crossed it, and if not, the age you will. Everything runs in today’s dollars, so the results read the way you actually think about money.
Coast FIRE Calculator
Find your coast FIRE number: the balance that grows into a fully funded retirement on its own, with no further contributions.
Projections use a constant real return (your nominal return net of inflation) and your chosen withdrawal rate. Markets do not deliver constant returns, and no projection is a guarantee. Figures are in today's dollars, before tax. This is an educational tool, not investment advice; talk to a fiduciary advisor before acting on it.
How to Calculate Your Coast FIRE Number
The math behind coast FIRE takes three steps. First, your FIRE number: annual retirement spending divided by your safe withdrawal rate, so $60,000 a year at 4% means $1,500,000. Second, the real return: a 7% expected return with 3% inflation nets out to about 3.88%, which is what your money grows by in purchasing power. Third, divide the FIRE number by your target retirement age growth factor. Over 35 years, 3.88% compounds to about 3.79x, so to calculate your coast FI number you divide $1,500,000 by 3.79 and get roughly $395,000. Have that invested at 30 and compound growth alone carries you to full financial independence at 65.
The same coast fire calculations run in reverse for planning. Today’s balance times the growth factor shows what your money becomes by retirement with no additional contributions, and multiplying that by the withdrawal rate shows the retirement spending it supports. A 30 year old with $100,000 is about 25% of the way to the coast threshold: growing but not yet free to stop.
Time is the whole trade. Here is the same divisor worked out per $1,000,000 of final target at a 3.88% real return:
| Years of growth remaining | Growth factor | Needed today per $1M target |
|---|---|---|
| 10 | 1.46x | $683,179 |
| 15 | 1.77x | $564,679 |
| 20 | 2.14x | $466,733 |
| 25 | 2.59x | $385,777 |
| 30 | 3.14x | $318,862 |
| 35 | 3.79x | $263,555 |
| 40 | 4.59x | $217,840 |
Coast FI vs Other Flavors of FIRE
The FIRE movement splits into flavors, and most FIRE calculators only handle the first one. Traditional FIRE means saving hard until your portfolio hits the full number, then quitting entirely; lean FIRE does it on a thin budget, fat FIRE on a generous one, and barista FIRE covers the gap with part-time work. Coast FI asks a gentler question: how much do you need invested now so that time does the rest? Once you reach the coast fire threshold, your paycheck only has to cover current expenses. You keep working, but the pressure of saving for retirement evaporates, which is why people describe crossing it as the first real taste of financial freedom, years before any resignation letter.
That is also what makes the coast fire strategy realistic for people who like their careers. You are not retiring at 38. You are buying the option to downshift, switch to meaningful work, or absorb a layoff without derailing retirement planning.
Your FI Number, Inflation, and the Real Return
Two assumptions drive everything. Your FI number depends on expenses in retirement, not on your income, so track what a year of your life costs before trusting any output. And because the threshold leans on decades of compounding, inflation matters more here than in almost any other projection. This tool handles it by discounting: the 7% default return becomes a 3.88% real return, and every figure stays in today’s dollars. The 4% figure itself traces to the Trinity study and William Bengen’s work in the 1990s, which tested withdrawal strategies against every historical 30 year market window; it held even through retirements that began in 1929 and 1966. If you prefer conservative coast fire calculators, drop the return to 5 or 6%, raise inflation, or use a 3.5% withdrawal rate; your coast fi number rises and the plan gets sturdier. Small changes swing the result by six figures over 35 years, which is honest, because the future really is that uncertain.
The Projection: When Can You Stop Saving?
If you are short of the threshold, the calculator projects forward month by month using your contribution. The target moves as you go: the balance you need to coast rises every year, since fewer years until retirement remain for compound interest to work. At the defaults, a 30 year old with $100,000 investing $2,000 a month reaches coast FI at about 46.7, then could stop contributing and still retire fully funded at 65. The word “could” matters. Most people who reach coast fi keep going anyway, because additional contributions past the line convert into an earlier retirement date or fatter spending, and because sequence risk rewards a margin of safety.
If the projection shows you never crossing before your target date, the breakdown says so plainly and shows where you land instead. The fixes are the honest ones: invest more, trim the annual spend assumption, or push the date.
Portfolio Assumptions in This Coast FIRE Calculator
The model assumes one blended portfolio earning a constant real return, which is a simplification in your favor to understand. Real markets deliver lumpy returns, and a bad decade early in the coast phase can put you behind the curve even when the long-run average holds. Count only true existing investments in the starting balance: retirement accounts like your 401(k) and IRA plus taxable brokerage money, not home equity or your emergency fund. The 4% safe withdrawal rate comes from research on a 30-year retirement; an early retirement stretching 40 or 50 years argues for 3 to 3.5% instead. Sequence of returns is the sharpest edge. Two decades that average 7% can arrive as a strong first half and a weak second, or the reverse, and the ending balances differ enormously even though the average matched. That risk cuts hardest right around the date you begin withdrawals, which is why many planners shift the mix gradually toward bonds in the final decade while keeping enough stocks to outpace rising prices for the following thirty years. A written allocation policy, rebalanced on a calendar rather than on emotion, matters more to the outcome than another decimal on the return assumption. And remember the tax layer this tool ignores: money in pre-tax accounts is worth less than its sticker price, so fat balances there deserve a haircut.
From Coast FI to Full Retirement and Financial Independence
Coasting is a milestone on the journey to financial independence, not the finish line. The sequence usually runs: hit your coast number, keep working with lighter savings, watch the investment growth do the heavy lifting, then reach your full FIRE number somewhere near the traditional retirement age you picked. Your full retirement number is the same figure whichever path you take; coasting just changes who funds it, you or compounding. Check in yearly. If markets ran hot you may be ahead of schedule; after a crash you may need to resume retirement contributions for a while. The calculator makes the re-check a 30 second habit rather than a spreadsheet project.
Frequently Asked Questions
What does reaching coast FIRE actually change?
One thing: you no longer need to save for retirement. Every earned dollar can go to living now, and the choice to stop saving becomes yours rather than the math’s.
Why does my coast number look so much smaller than my FIRE number?
Decades of compounding. At a 3.88% real return, money invested at 30 nearly quadruples in purchasing power by 65, so you only need about a quarter of the final figure up front. What coast fire means, in one line, is letting that multiplier replace your savings rate.
Can I use this as a coast FI calculator for barista FIRE?
Yes. That flavor is the same invested-asset math with part-time income covering current bills. Run the interactive calculator with your numbers, and if part-time work also covers some saving, you will cross the line sooner than projected.
Is the estimate guaranteed?
No. This coast fire calculator helps you find your coast fire number under fixed assumptions; markets, inflation, and your own spending will drift. Treat the output as a planning anchor you revisit yearly, and talk to a fiduciary advisor before making moves like cutting savings to zero.