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ConceptsRetirement PlanningGetting Started15 min readPublished March 14, 2026

Coast FIRE Calculator: Find Your Coast Number at Every Age

Calculate your Coast FIRE number with step-by-step formulas, comprehensive tables by age, and three worked examples. Find out if you have already reached Coast FIRE and what to do next.

What Is Your Coast FIRE Number?

Your Coast FIRE number is the amount you need in your investment portfolio today so that, with zero additional contributions, compound growth alone will carry it to your full financial independence target by your desired retirement age. Once you hit this number, saving for retirement becomes optional. You only need to earn enough to cover current living expenses.

If you are new to the concept, the Coast FIRE conceptual guide covers the philosophy, psychological benefits, and how Coast FIRE compares to Barista FIRE and Lean FIRE. This guide is purely practical: formulas, tables, and worked calculations you can use to find your own number.

The core formula discounts your FI number back to the present using your expected real investment return and the number of years remaining until retirement:

Coast FIRE Number=FI Number(1+r)n\text{Coast FIRE Number} = \frac{\text{FI Number}}{(1 + r)^n}

where rr is your expected annual real return (after inflation) and nn is the number of years until your target retirement age.

Calculate Your Coast Number

Coast FIRE Calculator

Current Age30
Retirement Age60
Annual Spending$50K
Current Portfolio$200K
Expected Real Return5%

$289K

Coast Number

$1.25M

FI Number at Retirement

$89K to go

Status

Current PortfolioCoast Number: $289K
$200K69%

Not yet coasting. You need $89K more to reach your Coast FIRE number. Without additional contributions, your current portfolio would grow to $864K by age 60, falling short of your $1.25M FI target.

Model your Coast FIRE trajectory with custom growth curves and milestone dates using Summitward's projections tool.

How to Calculate Your Coast FIRE Number

Follow these four steps to arrive at your personal Coast FIRE number.

Step 1: Determine Your FI Number

Your FI number is the portfolio size that can sustain your annual spending indefinitely through safe withdrawals. See the FI number guide for details. The formula is:

FI Number=Annual SpendingSafe Withdrawal Rate\text{FI Number} = \frac{\text{Annual Spending}}{\text{Safe Withdrawal Rate}}

For example, if you spend $80,000 per year and use a 4% safe withdrawal rate:

FI Number=$80,0000.04=$2,000,000\text{FI Number} = \frac{\$80{,}000}{0.04} = \$2{,}000{,}000

Step 2: Choose a Real Return Rate

Use the real (inflation-adjusted) return, not the nominal return. For a diversified stock portfolio, historical real returns have averaged roughly 6-7% before fees. After accounting for a more conservative outlook and investment costs, most planners use 4-6% as a reasonable range. A 5% real return is the most common assumption, balancing optimism with caution.

Why real and not nominal? Because your FI number is expressed in today's dollars. If you discount with nominal returns (say 10%), you would dramatically undercount how much you actually need today. The section on return assumptions below shows exactly how much this matters.

Step 3: Determine Years to Retirement

Subtract your current age from your target retirement age. For example, if you are 32 and targeting retirement at 60, you have 28 years of compounding runway.

n=Retirement Age−Current Age=60−32=28n = \text{Retirement Age} - \text{Current Age} = 60 - 32 = 28

Step 4: Apply the Coast FIRE Formula

Plug your values into the formula. Using the example above ($2M FI number, 5% real return, 28 years):

Coast FIRE=$2,000,000(1.05)28=$2,000,0003.920=$510,204\text{Coast FIRE} = \frac{\$2{,}000{,}000}{(1.05)^{28}} = \frac{\$2{,}000{,}000}{3.920} = \$510{,}204

If this 32-year-old has $510,204 invested today and never adds another dollar, the portfolio should grow to $2 million (in today's purchasing power) by age 60.

Coast FIRE by Age

The table below is the centerpiece of this guide. It shows Coast FIRE numbers for ages 25 through 55, targeting retirement at age 60, using a 5% real return. Three FI targets are shown to cover a range of spending levels.

Current AgeYears to 60Growth FactorFI Target $1MFI Target $1.5MFI Target $2M
25355.52x$181,300$271,900$362,500
27335.00x$200,000$300,000$400,000
30304.32x$231,400$347,100$462,800
32283.92x$255,100$382,600$510,200
35253.39x$295,300$443,000$590,600
37233.07x$325,600$488,500$651,300
40202.65x$376,900$565,300$753,700
42182.41x$415,500$623,300$831,000
45152.08x$481,000$721,500$962,100
47131.89x$530,300$795,500$1,060,700
50101.63x$613,900$920,900$1,227,800
5281.48x$676,800$1,015,300$1,353,700
5551.28x$783,500$1,175,300$1,567,100

Notice how dramatic the difference is between ages. A 25-year-old needs only $362,500 to coast to a $2M FI target, while a 50-year-old needs $1,227,800 for the same goal. The 25-year-old's compounding runway does most of the heavy lifting. Every year of delay makes the number harder to reach, which is why early saving is so powerful even if you plan to slow down later.

To use this table: find the row closest to your current age, then look at the column matching your FI target. If your invested portfolio (excluding home equity, emergency fund, and non-invested assets) meets or exceeds that number, you are Coast FIRE.

How Return Assumptions Change Everything

The 5% real return used above is a reasonable central estimate, but small changes in the assumed return rate have large effects over long time horizons. The table below shows how Coast FIRE numbers shift for a 35-year-old targeting retirement at 60 with a $1.5M FI target.

Real ReturnGrowth Factor (25 yrs)Coast FIRE NumberDifference vs. 5%
4%2.67x$562,400+$119,400 (+27%)
5%3.39x$443,000baseline
6%4.29x$349,700-$93,300 (-21%)
7%5.43x$276,200-$166,800 (-38%)

A single percentage point in either direction changes the Coast FIRE number by roughly 20-30%. This is why the return assumption is the most important input in the entire calculation. Here are some guidelines for choosing yours:

  • 4% real return: Conservative. Appropriate if you hold a balanced portfolio (60/40 stocks/bonds) or want extra margin of safety.
  • 5% real return: Moderate. A reasonable assumption for a diversified equity-heavy portfolio (80-90% stocks) over 20+ year horizons.
  • 6% real return: Optimistic. Reflects historical U.S. equity averages, but does not account for lower future return expectations some forecasters project.
  • 7% real return: Aggressive. Only appropriate if you hold 100% equities and are comfortable with significant volatility. Not recommended for planning purposes.

Real vs. Nominal Returns: Why This Matters

A nominal return includes inflation; a real return strips it out. If stocks return 10% nominally and inflation is 3%, the real return is approximately 7%. Since your FI number is in today's dollars, you must use real returns to keep the math consistent.

Using nominal returns is the single most common Coast FIRE calculation error. With a 10% nominal return, a 30-year-old would calculate:

Nominal: $2,000,000(1.10)30=$2,000,00017.449=$114,600\text{Nominal: } \frac{\$2{,}000{,}000}{(1.10)^{30}} = \frac{\$2{,}000{,}000}{17.449} = \$114{,}600
Real (5%): $2,000,000(1.05)30=$2,000,0004.322=$462,800\text{Real (5\%): } \frac{\$2{,}000{,}000}{(1.05)^{30}} = \frac{\$2{,}000{,}000}{4.322} = \$462{,}800

The nominal calculation suggests you only need $114,600, when you actually need $462,800. That is a 4x error that could leave you dramatically underfunded at retirement.

Three Worked Examples

Example A: 28-Year-Old Engineer with RSUs

Priya is 28, earns $160,000 in base salary plus $40,000 in annual RSU vests. She spends $80,000 per year (including taxes on RSU income) and wants to retire at 60. She uses a 4% safe withdrawal rate and a 5% real return.

Step 1: FI Number

FI Number=$80,0000.04=$2,000,000\text{FI Number} = \frac{\$80{,}000}{0.04} = \$2{,}000{,}000

Step 2: Years to retirement

n=60−28=32 yearsn = 60 - 28 = 32 \text{ years}

Step 3: Coast FIRE Number

Coast FIRE=$2,000,000(1.05)32=$2,000,0004.765=$419,700\text{Coast FIRE} = \frac{\$2{,}000{,}000}{(1.05)^{32}} = \frac{\$2{,}000{,}000}{4.765} = \$419{,}700

Priya has $310,000 currently invested (including $85,000 in company stock from vested RSUs). She is $109,700 short of her Coast FIRE number. At her current savings rate of $50,000 per year, she will reach Coast FIRE in roughly two more years.

One important consideration: if a large share of Priya's portfolio is concentrated in company stock, she may want to diversify. See the concentration risk guide for the sell-vs-hold framework.

Example B: 35-Year-Old with Family

Marcus is 35, married with two young children. The household spends $100,000 per year and he expects that to stay roughly constant in real terms (education costs will rise but commuting costs will eventually fall). He targets retirement at 62 and uses a 3.5% safe withdrawal rate for a longer retirement horizon.

Step 1: FI Number

FI Number=$100,0000.035=$2,857,143\text{FI Number} = \frac{\$100{,}000}{0.035} = \$2{,}857{,}143

Step 2: Years to retirement

n=62−35=27 yearsn = 62 - 35 = 27 \text{ years}

Step 3: Coast FIRE Number

Coast FIRE=$2,857,143(1.05)27=$2,857,1433.733=$765,400\text{Coast FIRE} = \frac{\$2{,}857{,}143}{(1.05)^{27}} = \frac{\$2{,}857{,}143}{3.733} = \$765{,}400

Marcus has $520,000 invested across a mix of 401(k), Roth IRA, and taxable accounts. He is $245,400 away from Coast FIRE. At a household savings rate of $60,000 per year (with employer 401(k) match included), he should reach Coast FIRE in about four years, around age 39.

Notice the impact of the lower 3.5% SWR. It pushes the FI number up to nearly $2.9M, which raises the Coast FIRE number significantly. The safe withdrawal rate you choose for your FI number flows directly through to your Coast FIRE calculation.

Example C: 42-Year-Old Late Starter

Dana is 42 and started serious investing only five years ago. She spends $60,000 per year, uses a 4% SWR, and targets retirement at 65. She uses a slightly more conservative 4.5% real return because her portfolio is 70/30 stocks and bonds.

Step 1: FI Number

FI Number=$60,0000.04=$1,500,000\text{FI Number} = \frac{\$60{,}000}{0.04} = \$1{,}500{,}000

Step 2: Years to retirement

n=65−42=23 yearsn = 65 - 42 = 23 \text{ years}

Step 3: Coast FIRE Number

Coast FIRE=$1,500,000(1.045)23=$1,500,0002.752=$545,200\text{Coast FIRE} = \frac{\$1{,}500{,}000}{(1.045)^{23}} = \frac{\$1{,}500{,}000}{2.752} = \$545{,}200

Dana has $285,000 invested. She is $260,200 short. At her savings rate of $30,000 per year (assuming 4.5% real growth on contributions), she will likely reach Coast FIRE around age 49. While that is later than the other examples, it still gives her 16 years of "coasting" before retirement. That is 16 years where she could drop to a lower-paying job, go part-time, or pursue other interests without jeopardizing her retirement trajectory.

Am I Already Coast FIRE?

To check whether you have already reached Coast FIRE, follow these three steps:

  1. Calculate your Coast FIRE number using the formula above (or find your row in the age table).
  2. Tally your invested portfolio. Include 401(k), IRA, Roth IRA, taxable brokerage accounts, and HSA balances. Exclude home equity, emergency funds, cash reserves, and any assets you do not plan to draw from in retirement.
  3. Compare. If your invested portfolio is greater than or equal to your Coast FIRE number, you are Coast FIRE.

If You Are Already Coast FIRE

Congratulations. This means compound growth is projected to handle the rest. You have several options:

  • Keep saving. Continued contributions accelerate your timeline to full FI. You will reach it years earlier than the coast projection suggests.
  • Reduce hours or take a pay cut. You only need to cover current expenses. A lower-stress job or reduced schedule becomes financially viable.
  • Redirect savings to near-term goals. Instead of putting every spare dollar into retirement accounts, you could fund a sabbatical, a career transition, or a home purchase.
  • Do nothing differently. Many people find that simply knowing they are Coast FIRE reduces financial anxiety, even if they continue their current career path unchanged.

If You Are Not Yet Coast FIRE

Calculate the gap between your current portfolio and your Coast FIRE number. Then estimate how long it will take to close that gap at your current savings rate. The formula for time-to-Coast-FIRE when you are making regular contributions is more complex:

Future Value=P(1+r)t+C⋅(1+r)t−1r\text{Future Value} = P(1 + r)^t + C \cdot \frac{(1 + r)^t - 1}{r}

where PP is your current portfolio, CC is your annual contribution, rr is the real return, and tt is the number of years. Solve for tt when Future Value equals the Coast FIRE number for your age at that future date (which itself decreases as you age, making the target a moving one that gets closer as you approach it).

Coast FIRE with Different Retirement Ages

The tables above all assume retirement at age 60. But your target retirement age has a dramatic effect on the Coast FIRE number. The table below shows how the Coast FIRE number changes for a person with a $1.5M FI target and 5% real return, depending on both their current age and their target retirement age.

Current AgeRetire at 55Retire at 60Retire at 65
25$352,600$271,900$209,700
30$450,100$347,100$267,700
35$574,700$443,000$341,700
40$733,600$565,300$436,200
45$936,600$721,500$556,700
50$1,195,700$920,900$710,700
55$1,500,000$1,175,300$907,000

A 35-year-old targeting retirement at 55 needs $574,700 in today's portfolio, but the same person targeting 65 needs only $341,700. That is a $233,000 difference for shifting retirement by just 10 years. If you are flexible on your retirement age, you may already be Coast FIRE for a later target even if you are not for an earlier one.

This table also reveals an important dynamic: at age 55 targeting retirement at 55, the Coast FIRE number equals the full FI number ($1.5M). That makes sense, because there are zero years of compounding remaining. Coast FIRE only provides leverage when you have time on your side.

Limitations of the Coast FIRE Calculation

The Coast FIRE formula is elegant and useful, but it rests on simplifying assumptions that you should understand before relying on it as your primary planning tool.

Single Return Rate Assumption

The formula assumes your portfolio grows at a smooth, constant rate every year. In reality, markets are volatile. A portfolio might return +22% one year and -15% the next. Sequence of returns matters: a major downturn shortly after you stop contributing can delay your Coast FIRE projection significantly, even if long-run average returns match your assumption.

For a more robust approach, Monte Carlo simulation tests thousands of possible return sequences and gives you a probability of reaching your FI target, not just a single point estimate. A 90% success probability across 10,000 simulated scenarios is far more informative than a single deterministic projection.

Inflation Risk

Using real returns accounts for average inflation, but inflation is not constant. A prolonged period of above-average inflation (such as 2021-2023) erodes real returns and pushes your Coast FIRE date out. If you are concerned about inflation risk, consider using a slightly lower real return assumption (4% instead of 5%) as a buffer.

Spending Changes Over Time

The calculation assumes your spending stays constant in real terms. In practice, spending shifts throughout life: it may rise when you have children or take on a mortgage, and fall after kids leave home and the mortgage is paid off. If your spending increases, your FI number increases, which raises your Coast FIRE number retroactively. Revisit the calculation annually.

The Healthcare Gap

If you leave a corporate job to "coast" on lower-paid or part-time work, you may lose employer-sponsored health insurance. In the U.S., individual or family coverage through the ACA marketplace can cost $500 to $2,000+ per month depending on your age, location, and family size. This cost must be factored into the expenses you need your coast-phase income to cover. Many people underestimate this gap.

Tax Considerations

The formula does not distinguish between pre-tax and after-tax accounts. In practice, the tax treatment of your accounts affects both your FI number and your withdrawal strategy. A portfolio split across traditional 401(k), Roth IRA, and taxable accounts will have different effective withdrawal rates than a single-account portfolio. Consider your Roth conversion strategy as part of your overall plan.

Key Takeaways

  • The formula is simple but powerful. Coast FIRE Number = FI Number / (1 + r)^n. Three inputs (FI target, real return, years to retirement) give you a concrete savings target.
  • Age is the dominant variable. A 25-year-old needs roughly half the portfolio of a 35-year-old to coast to the same FI target. Every year of earlier saving dramatically reduces the amount you need.
  • The return assumption matters more than you think. A single percentage point change in real return shifts the Coast FIRE number by 20-30% over a 25-year horizon. Be deliberate about your assumption and understand the range of outcomes.
  • Always use real (inflation-adjusted) returns. Using nominal returns can understate your needed portfolio by 3-4x. Since your FI number is in today's dollars, the discount rate must also be in real terms.
  • Coast FIRE is a waypoint, not a destination. It tells you when you can stop saving, not when you can stop working. You still need income to cover current expenses. But it opens the door to lower- stress work, career changes, and reduced hours.
  • Supplement with Monte Carlo analysis. The deterministic formula gives a useful estimate, but a Monte Carlo simulation accounts for return volatility, sequence risk, and gives you probability-based confidence in your plan.

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