Coast FIRE Calculator

Coast FIRE Explained: The Math, the Strategy, and the Life It Unlocks

Most personal finance advice treats retirement savings as a lifelong obligation — contribute steadily from your first paycheck to your last, then live off what you’ve built. Coast FIRE challenges that assumption entirely. The central insight is simple: if you can accumulate a meaningful amount of invested assets early enough in your career, compound interest will carry you to your retirement goal without requiring a single additional dollar from your paycheck. You “coast” from that point — covering your current living expenses through work, but no longer needing to race toward any savings target. The result is a dramatic shift in how you think about your job, your spending, and your freedom.

How to Calculate Your Coast FIRE Number — The Exact Formula

The Coast FIRE calculation begins with your Full FIRE Number. Using the 4% Safe Withdrawal Rate established by Bengen (1994) and validated by the Trinity Study (1998), your Full FIRE Number is simply your expected annual retirement spending divided by 0.04 — or equivalently, multiplied by 25. If you expect to spend $60,000 per year in retirement, your Full FIRE Number is $1,500,000. Once you have that target, you work backward to today using the present value of money formula: Coast FIRE Number = Full FIRE Number ÷ (1 + real annual return)^years_to_retirement. The “real annual return” is your nominal investment return minus inflation — or more precisely, ((1 + nominal) ÷ (1 + inflation)) − 1. At 10% nominal return and 3% inflation, the real return is approximately 6.80%, not simply 7%. A 30-year-old targeting $1,500,000 at age 65 with a 6.80% real return needs approximately $177,000 invested today to coast to full financial independence with no further contributions.

Coast FIRE vs Barista FIRE — Understanding the Difference

Coast FIRE and Barista FIRE are frequently confused, and the distinction matters for your planning. Coast FIRE requires you to continue earning your full current living expenses from work — you just no longer need to contribute to retirement accounts. Your job need not be high-paying or career-advancing; you only need it to cover rent, food, transportation, and lifestyle costs. Barista FIRE goes one step further: your portfolio covers part of your retirement needs, and a part-time job (traditionally something low-stress, like working at a coffee shop — hence the name) covers the remainder. The Barista FIRE number is lower than Coast FIRE because it assumes you will supplement your portfolio’s income with ongoing work income. For example, if your annual retirement spending is $60,000 and a part-time role earns $20,000 per year, your Barista FIRE portfolio only needs to replace $40,000 annually — meaning a $1,000,000 target rather than $1,500,000. Both strategies are significantly more accessible than full FIRE, which requires funding 100% of expenses from your portfolio with zero income.

Coast FIRE by Age — Why Starting Early Is Exponentially More Valuable

The compounding math behind Coast FIRE creates a dramatic advantage for early starters that cannot be replicated by saving more later. At a 7% real return with a $1,500,000 retirement goal (age 65): a 25-year-old needs approximately $147,000 in today’s dollars. A 30-year-old needs $197,000. A 35-year-old needs $276,000. A 40-year-old needs $388,000. A 45-year-old needs $544,000. A 50-year-old needs $764,000. Every five years of delay increases the required Coast FIRE number by approximately 40%. This is not linear — it is exponential. The practical implication is that aggressive saving in your 20s — even at a modest income — can create a Coast FIRE foundation that a high earner starting at 40 would struggle to replicate. A 26-year-old who saves $150,000 before their 30th birthday and then never contributes again will likely retire with over $1.5 million at 65 (at 7% real return). No amount of catch-up contributions can buy back those early compounding years.

Is Coast FIRE Realistic? What the Data Actually Shows

The question of whether Coast FIRE is realistic depends almost entirely on when you start. For workers who begin investing seriously in their mid-20s with even a moderate income, Coast FIRE is not just realistic — it is achievable within 5–10 years of entering the workforce with disciplined saving. The S&P 500 has returned approximately 10% per year nominally since 1926 (Stern NYU Damodaran data) or 7% annually in real (inflation-adjusted) terms. Over any 30-year period in modern US financial history, a diversified stock index portfolio has never failed to produce meaningful real growth. The risks that make Coast FIRE less certain are: (1) sequence-of-returns risk in the years approaching retirement — a significant market downturn in your final 5–10 years before retiring can materially reduce your portfolio; (2) lifestyle inflation that pushes expected retirement spending above your original estimate; and (3) unexpected life events (disability, medical costs, family obligations) that interrupt the coasting phase. Addressing these with a slightly more conservative withdrawal rate (3.5% instead of 4%), a conservative return assumption (6% instead of 7%), and some continued voluntary saving after reaching Coast FIRE makes the strategy significantly more robust.

The Best Investments for Coast FIRE — Low Fees Make the Biggest Difference

Once you have determined your Coast FIRE number and are working toward it, the single most controllable variable — besides your savings rate — is your investment expense ratio. The difference between a 1.0% annual fee and a 0.18% Vanguard index fund expense ratio, compounded over 30 years on a $200,000 portfolio, amounts to approximately $220,000 in lost wealth. For Coast FIRE, where compound interest does all the heavy lifting after a certain point, minimizing fees is not a minor optimization — it is a structural advantage. The evidence-based approach widely used in the FIRE community combines broad-market index funds (total US market, total international market), target-date funds, or simple three-fund portfolios (US stocks, international stocks, bonds). Dollar-cost averaging into these low-cost vehicles during the accumulation phase, then switching to a more conservative allocation as you approach your retirement coast date, is the standard playbook. Avoid actively managed funds, variable annuities, and any investment product with an expense ratio above 0.5%.

Coast FIRE and Taxes — How to Maximize Your After-Tax Returns

The tax efficiency of your Coast FIRE portfolio significantly affects how quickly you reach your number. Roth IRA contributions grow tax-free and are withdrawn tax-free in retirement — an enormous advantage for long coast periods. Traditional 401(k) and IRA contributions reduce your current taxable income (valuable during high-earning years) but are taxable at withdrawal. For Coast FIRE practitioners who will work lower-paying jobs after reaching their coast number, tax planning becomes nuanced: lower income years offer an opportunity to do Roth conversions at lower tax rates, moving money from taxable traditional accounts to tax-free Roth accounts. Use our Income Tax Calculator → to understand your current bracket and model the after-tax impact of your retirement contributions. Understanding your effective tax rate also helps you determine whether traditional or Roth contributions are more advantageous during your accumulation phase — a choice that can meaningfully affect your after-tax Coast FIRE number.