Coast FIRE Calculator: How Much to Save Before You Stop

Coast FIRE Calculator: How Much to Save Before You Stop

There is a version of financial independence that does not require you to grind until your portfolio hits some massive number before you can breathe. It is called Coast FIRE, and once you understand the math behind it, it changes the way you think about saving entirely. The core idea is simple: save aggressively early, let compound interest do the heavy lifting, and eventually reach a point where you can stop contributing to retirement accounts altogether — your existing balance will coast to your target by itself.

I’ve spent a lot of time researching this topic, and here’s what I found.

Related: index fund investing guide

For knowledge workers in their twenties, thirties, and forties — people with decent incomes but also real cognitive load, career pressure, and life happening all around them — Coast FIRE offers something genuinely practical. You do not have to save forever. You just have to save enough, early enough. Then you can redirect that capital toward present-day quality of life, a lower-stress job, or whatever matters most to you now.

Let us break down exactly how to calculate your Coast FIRE number, what assumptions matter most, and how to actually use this information without turning it into another source of financial anxiety.

What Coast FIRE Actually Means

Coast FIRE sits within the broader FIRE (Financial Independence, Retire Early) movement, but it occupies a distinct and arguably more accessible position. Traditional FIRE requires you to accumulate 25 times your annual expenses — a figure derived from the 4% safe withdrawal rate established by Bengen (1994) and later confirmed by the Trinity Study. Coast FIRE asks a different question: at what point does your current portfolio, left untouched and growing at a market rate, reach that 25x number by your target retirement age?

Once you hit your Coast FIRE number, your investments do the saving for you. You still need to earn enough to cover your current living expenses, but the retirement funding pressure is gone. Many people use this milestone as permission to change careers, go part-time, take on consulting work, or simply stop obsessing over maximizing every contribution. It is a psychological and financial checkpoint, not a finish line.

The term “coasting” is deliberate. Your portfolio is doing the work. You are just staying afloat in a job that covers today without worrying about tomorrow.

The Math: How the Coast FIRE Calculator Works

The calculation has three inputs: your target retirement number, your expected rate of return, and the number of years until retirement. From those three variables, you can work backward to find your Coast FIRE number today.

The formula is:

Coast FIRE Number = Retirement Target ÷ (1 + r)ⁿ

Where r is your annual real rate of return and n is the number of years until retirement.

Let us walk through a realistic example. Suppose you spend $60,000 per year and expect to spend similarly in retirement. Your retirement target using the 4% rule is $1,500,000. You are 32 years old and plan to retire at 62, giving you 30 years of growth. You assume a real (inflation-adjusted) annual return of 5%, which is a conservative but defensible long-run estimate for a diversified equity portfolio (Dimson, Marsh, & Staunton, 2002).

Coast FIRE Number = $1,500,000 ÷ (1.05)³⁰

Coast FIRE Number = $1,500,000 ÷ 4.322

Coast FIRE Number ≈ $347,000

If you have $347,000 saved at age 32 and never contribute another dollar, that portfolio will grow to approximately $1,500,000 by age 62 in real terms. You have effectively pre-funded your retirement. Everything you earn from this point forward just needs to cover your current lifestyle.

Choosing Your Rate of Return Assumption

This is where most Coast FIRE calculations go wrong. People plug in 7%, 8%, or even 10% nominal returns because those numbers appear in popular financial media. But there are two critical adjustments to make.

First, use a real return rather than a nominal one. Inflation erodes purchasing power, and your retirement spending target is in today’s dollars. The historical real return of U.S. equities over the long run has been approximately 6.5–7%, but international diversification typically pulls that figure lower for a globally diversified portfolio (Dimson et al., 2002). A real return assumption of 5% to 6% is both honest and defensible for planning purposes.

Second, recognize that sequence-of-returns risk matters more when you are approaching retirement, not during the coasting phase. During the coasting phase, you are not withdrawing anything, so volatility is actually your friend — it does not matter when the market dips as long as the long-run average holds. This is one reason Coast FIRE calculations are somewhat more forgiving than traditional accumulation targets.

A reasonable approach: use 5% real for a conservative plan, 6% real for a moderate plan, and compare both. If your Coast FIRE number is achievable under the 5% assumption, you are in solid shape.

What About Your Retirement Target?

The 25x rule (equivalently, the 4% withdrawal rate) has been both validated and challenged since its original formulation. Bengen (1994) found that a 4% initial withdrawal rate, adjusted for inflation annually, survived every 30-year retirement period in U.S. historical data. More recent research suggests that for longer retirements — say, 40 or 50 years — a 3.5% or 3.3% rate offers more margin (Pfau, 2012).

For knowledge workers targeting early retirement, this matters. A 35-year-old planning to stop working at 55 faces a potential 40-plus-year retirement. Using 25x ($1,500,000 on $60,000 spending) might be slightly optimistic. Using 30x ($1,800,000) adds meaningful buffer and is worth considering if you want to be conservative.

The practical takeaway: do not obsess over the exact multiple, but understand that younger early retirees should lean toward a slightly higher multiple than the classic 25x. Running your Coast FIRE calculation with both 25x and 30x targets gives you a useful range.

Building Your Own Coast FIRE Calculation

You do not need a fancy tool. A spreadsheet or even a basic calculation handles this cleanly. Here is how to approach it systematically.

Step 1 — Establish Your Annual Retirement Spending

Track your current spending with some care. Not just rough estimates — actual categories. Research on consumer behavior suggests that people systematically underestimate discretionary spending when relying on memory rather than records (Kahneman, 2011). Pull three months of bank and credit card statements and calculate a realistic monthly figure, then annualize it. Some expenses will decrease in retirement (commuting, professional clothing, lunch costs), others may increase (healthcare, travel, hobbies). Build in a realistic adjustment rather than assuming you will spend dramatically less.

Step 2 — Calculate Your Retirement Target

Multiply your annual retirement spending by your chosen multiple. If you spend $70,000 per year and use a 28x multiple (a 3.6% withdrawal rate, which splits the difference between conservative and standard), your target is $1,960,000. Round to $2,000,000 for simplicity and psychological clarity.

Step 3 — Determine Your Time Horizon

Choose your target retirement age. Be realistic but also generous with yourself. If you are 30 and want to retire at 55, that is 25 years. If you are 40 and aiming for 65, that is 25 years as well. The time horizon is one of the most powerful variables in this calculation — an extra five years of compounding dramatically reduces the Coast FIRE number you need today.

Step 4 — Apply the Formula

Divide your retirement target by (1 + real return rate) raised to the power of your time horizon. The result is your Coast FIRE number — the portfolio value you need right now, today, for your existing savings to grow to your retirement target without any additional contributions.

Step 5 — Compare to Your Current Portfolio

Log into your retirement accounts and add up the balances. Include taxable brokerage accounts if you have them. Do not include your emergency fund or home equity in this calculation — those serve different purposes. How does your current total compare to your Coast FIRE number? If you are above it, you have officially coasted. If you are below, you now know exactly how much further you need to go and can work backward to a monthly savings goal.

The Role of Time: Why Starting Early Is Not a Cliché

The reason Coast FIRE is so powerful for younger savers is purely mathematical. Consider two people with the same retirement target of $1,500,000 and the same 5% real return assumption. Person A is 25 and plans to retire at 65 — a 40-year horizon. Person B is 35 and plans to retire at 65 — a 30-year horizon.

• Person A (40 years): $1,500,000 ÷ (1.05)⁴⁰ = $1,500,000 ÷ 7.04 ≈ $213,000
• Person B (30 years): $1,500,000 ÷ (1.05)³⁰ = $1,500,000 ÷ 4.32 ≈ $347,000

Person A needs $134,000 less than Person B to reach the same outcome, purely because of an extra decade of compounding. This is why front-loading savings in your twenties and early thirties creates such disproportionate use. The math is not motivational rhetoric — it is exponential arithmetic.

For someone with ADHD or anyone who struggles with abstract future rewards, this reframing can actually help. Instead of “save as much as possible forever,” the goal becomes “hit this specific number as fast as possible, then stop.” That is a much more actionable, finite target — and finite targets are psychologically easier to pursue consistently (Kahneman, 2011).

Taxes, Account Types, and Real-World Friction

Coast FIRE calculations in their pure form ignore taxes, and that is a meaningful omission in practice. The account type where your savings live affects how your Coast FIRE number translates into actual retirement income.

Money in a traditional 401(k) or IRA grows tax-deferred but is taxed as ordinary income on withdrawal. A $1,500,000 traditional IRA does not produce $60,000 in after-tax income at a 4% withdrawal rate unless your effective tax rate in retirement is zero — which is possible but requires careful planning. Money in a Roth IRA grows and withdraws tax-free, making it much cleaner for this kind of calculation. Taxable brokerage accounts are taxed on dividends and capital gains annually, with more favorable long-term capital gains rates.

A practical rule of thumb: if the majority of your savings are in pre-tax accounts, add 15–25% to your Coast FIRE number to account for future tax drag. If you are primarily in Roth accounts, the base calculation holds more cleanly. Most knowledge workers in the 25–45 age range benefit from a mix of both, hedging against future tax rate uncertainty.

What to Do After You Coast

Reaching your Coast FIRE number does not mean the work is finished — it means the financial pressure changes shape. You no longer need to maximize retirement contributions, but you still need to cover current expenses. This is where many Coast FIRE adherents make a deliberate career pivot: they shift from high-paying, high-stress work toward work that covers the bills and provides meaning without requiring them to constantly optimize for income.

For knowledge workers, this often looks like consulting rather than full-time employment, moving into teaching or mentorship roles, building something entrepreneurial at a slower pace, or simply staying in a current role but negotiating reduced hours. The key insight is that you are no longer working for retirement — you are working to fund the present. That reorientation changes how you evaluate career decisions in ways that are genuinely difficult to overstate.

Some people find that after coasting, they actually enjoy working more because the financial desperation is gone. Research on motivation suggests that autonomy and intrinsic interest drive performance and satisfaction far more than external rewards once basic needs are met (Deci & Ryan, 2000). Removing the financial coercion from work often reveals what you actually want to spend your time doing.

Common Mistakes in Coast FIRE Planning

Several errors appear repeatedly when people run these calculations on their own.

Using nominal returns instead of real returns inflates the Coast FIRE number in your favor, making you think you are closer than you are. Always adjust for inflation or express both your retirement target and your return assumption in real terms.

Ignoring healthcare costs before Medicare eligibility is a serious oversight for anyone planning to stop working before 65. Health insurance premiums in the individual market are substantial and highly variable. Build this cost explicitly into your annual retirement spending estimate rather than hoping it averages out.

Treating Coast FIRE as a precise prediction rather than a probabilistic framework leads to false confidence. Markets do not return a smooth 5% per year — they are volatile, and long-run averages mask short-run turbulence. Run your calculation at multiple return assumptions and treat the result as a range, not a single answer.

Counting assets that cannot be easily liquidated inflates your apparent progress. Your primary home is not part of your investment portfolio for this purpose unless you plan to sell it and downsize. A paid-off home reduces future housing costs, which affects your spending estimate, but it should not be counted as part of your portfolio balance.

A Real Sense of What Is Achievable

For a 30-year-old knowledge worker earning $90,000 to $130,000 per year — a range that covers software developers, teachers in high-cost-of-living areas, mid-level managers, analysts, and similar roles — reaching a Coast FIRE number in the $300,000–$500,000 range within 10 to 15 years is achievable with disciplined but not extreme saving. That is not a trivial sum, but it is not an impossible one either, especially when employer matching, tax-advantaged account limits, and consistent investing are all working together.

The point is not that everyone will hit these numbers on the same timeline. The point is that the goal is concrete, calculable, and fundamentally different from the open-ended instruction to “save as much as you can for as long as you can.” Coast FIRE gives you a finish line for the heavy lifting phase, and that specificity is worth something — cognitively, motivationally, and practically.

Run the numbers with your actual spending, your actual return assumptions, and your honest target retirement age. The result will either confirm you are closer than you thought, or it will show you exactly how many years of aggressive saving remain between you and the coast. Either way, you will be working with clarity rather than vague financial dread — and that is the most productive place to make any decision about money.

Last updated: 2026-03-31

My take: the research points in a clear direction here.

Does this match your experience?

References

• Kitces, M. (2021). Helping Clients Understand When They Have Enough Retirement Savings To “Coast FIRE” (And Keep Working Without Having To Contribute More). Kitces.com. Link
• Bengen, W. P. (1994). Determining Withdrawal Rates Using Historical Data. Journal of Financial Planning. Link
• Cooley, P. L., Hubbard, C. M., & Walz, D. T. (1998). Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable. AAII Journal. Link
• Trinity Study Authors (1998). Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable. Referenced in multiple FIRE analyses. Link
• TD Asset Management (2023). Guide to CoastFIRE: The ETF Experience Podcast. TD.com. Link

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