The Number That Changes How You Think About Work
A 30-year-old with $140,000 invested and no further contributions will have roughly $1,500,000 at age 65. A 40-year-old with the same $140,000 who stops contributing will have only about $382,000. The ten-year head start produced nearly four times the ending balance without a single additional dollar invested.
That gap is what Coast FI is about. It tells you how much you need invested right now so that compound interest alone carries your portfolio to your full retirement number by your target age. Once you hit that threshold, you never need to save for retirement again. You only need to earn enough to cover your current living expenses.
The Federal Reserve's 2022 Survey of Consumer Finances (the latest available, with the next wave expected in late 2026) found that the median retirement account balance for households under 35 was just $18,880. For ages 35 to 44, it was $45,000. Most people are nowhere near their Coast FI number, but the math shows why closing that gap early matters more than almost any other financial decision you can make.
How the Math Actually Works
The Coast FI formula is present value math:
Coast FI Number = Target Retirement Portfolio / (1 + annual return rate)^years until retirement
Your target retirement portfolio is your full FIRE number, typically 25x your annual expenses using the 4% rule. The formula discounts that future target back to today using your expected investment return. The result is the minimum balance you need right now for compound growth to close the gap without further contributions.
Say you need $1,500,000 to retire. You plan to retire at 65 and you are 30, giving you 35 years. At 7% expected annual return:
Coast FI Number = $1,500,000 / (1.07)^35 = $1,500,000 / 10.68 = $140,450
If you have $140,450 invested at age 30 and never contribute another dollar, compound growth alone delivers approximately $1,500,000 by age 65. Your retirement is funded in principle. The only remaining task is not withdrawing the money and not interrupting the compounding.
A dollar invested at 30 grows to 10.68 dollars at 65 at 7%. A dollar invested at 50 grows to only 3.87 dollars. That asymmetry is why the Coast FI number for a 25-year-old is roughly $72,000 while the number for a 45-year-old is over $258,000.
Why Your Assumptions Matter
The return rate you input changes your Coast FI number dramatically. The S&P 500 has returned approximately 10.2% annually in nominal terms and about 7.0% after inflation since 1928, according to NYU Stern professor Aswath Damodaran's historical dataset. Over the past 30 years (1996 through 2025), the annualized return was 10.4%.
For Coast FI planning, use 6 to 7% as your return assumption. This accounts for inflation, investment fees, and the reality that future returns may not match the past decade's exceptional performance. Using 10% produces a misleadingly low Coast FI number that assumes every year will be a bull market. Using 7% gives you a number in today's purchasing power, which is the number that actually matters for planning.
Your retirement target matters just as much. A $40,000/year retirement lifestyle requires a $1,000,000 portfolio at 25x expenses. A $60,000/year lifestyle requires $1,500,000. If you can genuinely enjoy a retirement on $45,000/year instead of $65,000/year, your Coast FI number drops by roughly 30%.
Coast FI by Age: Reference Table
Assuming a $1,000,000 target retirement portfolio and 7% annual return (inflation-adjusted):
| Current Age | Years to 65 | Coast FI Number |
|---|---|---|
| 22 | 43 years | $58,200 |
| 25 | 40 years | $72,000 |
| 30 | 35 years | $94,000 |
| 35 | 30 years | $131,400 |
| 40 | 25 years | $184,200 |
| 45 | 20 years | $258,400 |
| 50 | 15 years | $362,400 |
| 55 | 10 years | $508,300 |
A 22-year-old who saves $58,200 by their mid-20s has effectively funded their entire retirement. Achieving that in the first few years of a career is realistic with a high savings rate and no student loans. It is achievable by the late 20s even with modest student debt if you live below your means and use tax-advantaged accounts.
For a $2,000,000 target, double all figures. For a $1,500,000 target, multiply by 1.5.
How to Reach Coast FI Faster
The retirement target is where the real advantage is. You have limited control over your current age and market returns, but you control your planned retirement lifestyle.
Lowering your target lifestyle in retirement reduces your Coast FI number proportionally. A $45,000/year retirement instead of $65,000/year drops your target from $1,625,000 to $1,125,000, and your Coast FI number drops with it.
Maximizing early contributions is the other lever. The math is unforgiving about time. $50,000 invested at 25 outperforms $50,000 invested at 35 by a massive margin. High savings rates in the first decade of your career are disproportionately powerful because those dollars get the most compounding years. In 2026, you can contribute up to $24,500 to a 401(k) and $7,500 to a Roth IRA, per the IRS 2026 contribution limits. Maxing both in your 20s can get you to Coast FI within five to seven years.
Tax-advantaged accounts also matter. Roth IRAs, 401(k)s, and HSAs grow without annual tax drag. Keeping investments in these accounts rather than a taxable brokerage effectively increases your real return rate, which lowers your Coast FI number.
Coast FI vs Other FIRE Milestones
The FIRE community uses several related terms. Understanding the distinction helps you pick the right target:
Lean FI: 25x your minimum acceptable annual expenses. You could retire now on a lean budget.
Coast FI: Enough invested that compound growth reaches full FI by retirement age without additional contributions.
Barista FI / Semi-Retirement: Enough invested to cover most expenses, but you work part-time or in a lower-stress job to cover the remainder. Learn more in our guide to Barista FI, Coast FI, and Lean FI.
Full FI: 25x your actual current annual expenses. You can retire now and sustain your current lifestyle indefinitely at a 4% withdrawal rate.
Coast FI is unique because it focuses on the present value of future financial independence rather than the current ability to retire. It is a runway calculation, not a cleared-for-takeoff calculation. For a broader projection, try our FIRE calculator or retirement number calculator.
Real-World Examples
Example: Jenna, 26, aggressive early saver
Situation: Jenna maxed her Roth IRA and 401(k) for three years after graduating. She has $85,000 invested. Her target retirement portfolio at 65 is $1,200,000.
Her Coast FI check: At 7% for 39 years (age 26 to 65), the present value factor is 14.97. $1,200,000 / 14.97 = $80,160 needed. She has $85,000.
Result: Jenna has already reached Coast FI at 26. Her retirement is mathematically secured by compound growth alone. She can drop to a 10% savings rate, change careers, or take a lower-paying job she enjoys more without derailing her retirement.
Example: Robert, 42, freelance designer starting late
Situation: Robert has $180,000 invested across a Roth IRA and a taxable brokerage account. His income fluctuates between $55,000 and $95,000 per year. He wants to retire at 67 with a $1,800,000 portfolio.
His Coast FI check: At 7% for 25 years, the present value factor is 5.43. $1,800,000 / 5.43 = $331,500 needed. He has $180,000.
His gap: $151,500 still to accumulate. Robert automates a baseline of $1,200/month to his accounts and manually sweeps an extra $500 to $800 when client invoices clear. At an average $1,500/month and 7% return, he reaches Coast FI in approximately 5.5 years, at age 47.
Result: Robert is not at Coast FI yet, but he has a clear timeline. He plans to maintain aggressive saving until 48, then transition to part-time consulting while his portfolio coasts the remaining 19 years to full FI at 67.
Common Pitfalls to Avoid
Using too high a return rate. The S&P 500 returned 14.8% annualized over the last 10 years (2016 through 2025), but that period included an extraordinary AI-driven bull market. Planning at 10% or higher ignores inflation, fees, and the possibility of a lost decade. The 2000s produced a negative annualized return. Use 6 to 7% for realistic planning.
Ignoring sequence of returns risk. If your portfolio drops 30% the year after you stop contributing, your Coast FI milestone gets pushed back by several years. This is why diversification matters even during the coast phase. A portfolio split between stocks and bonds will not grow as fast, but it will not fall as far either.
Forgetting about taxes in taxable accounts. The Coast FI formula assumes your full return compounds. In a taxable brokerage account, dividend distributions and rebalancing generate tax bills that reduce your effective return. Keep as much as possible in tax-advantaged accounts to minimize this drag.
Treating Coast FI as a license to stop earning. Coast FI means your retirement is funded. It does not mean you can stop paying for housing, food, healthcare, and insurance. You still need income to cover current expenses. The difference is that the income can come from a job you actually like rather than one that pays enough to fund retirement.
This calculator is for educational and informational purposes only and does not constitute financial advice. Coast FI projections use assumed investment return rates and the 4% withdrawal rule. Actual investment returns are not guaranteed. Consult a licensed financial advisor for personalized retirement planning.
