CoastFIRE Calculator 2026: Calculate Your Coast Number Instantly

Meta Title: CoastFIRE Calculator – Determine Your Coast Financial Independence Number
Meta Description: Calculate your CoastFIRE number and timeline. Determine if you can stop investing and coast to financial independence with our free calculator.

On This Page

• What Is CoastFIRE?
• How CoastFIRE Works
• Calculating Your Coast Number
• How to Use a CoastFIRE Calculator
• CoastFIRE Formula Explained
• CoastFIRE vs. Traditional FIRE
• Compound Interest and Coast Number
• Lifestyle Flexibility with CoastFIRE
• Tax Considerations for CoastFIRE
• Common CoastFIRE Calculator Mistakes
• FAQ: CoastFIRE Calculator

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What Is CoastFIRE?

CoastFIRE is a financial independence strategy where you accumulate enough invested capital that compound interest alone will grow it to your target retirement number. Once you reach your "coast number," you can stop investing entirely and let your money work for you.

For example: If you have $300,000 invested at age 40 and let it compound at 7% annually until age 65, it could grow to $2+ million without adding a single dollar more. That $300,000 is your coast number.

A CoastFIRE Calculator determines your exact coast number based on your target retirement goal, time horizon, and expected investment returns.

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How CoastFIRE Works

CoastFIRE involves three key phases:

Phase 1: Accumulation
You invest aggressively, building capital. This phase ends when you reach your coast number.

Phase 2: Coasting
You stop investing. Your money compounds passively. You can work part-time, pursue passion projects, or reduce work hours entirely.

Phase 3: Retirement
At your target retirement age, your coasted capital has grown to your full FI number. You retire completely.

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Calculating Your Coast Number

The coast number depends on:

• Your current age
• Your target retirement age
• Your retirement spending goal (or FI number)
• Your expected annual investment return

Simple Example

• Target FI: $1,000,000
• Retirement age: 65
• Current age: 40 (25 years to grow)
• Expected return: 7% annually

Working backward, your coast number ≈ $184,000. If you have $184,000 now, it grows to ~$1M by age 65 without additional contributions.

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How to Use a CoastFIRE Calculator

Step 1: Input Your Current Age
Enter your age today.

Step 2: Input Retirement Age
Specify when you want to stop working.

Step 3: Input Current Invested Capital
Enter how much you currently have invested.

Step 4: Input Retirement Target (FI Number)
Specify your target retirement savings goal.

Step 5: Input Expected Return
Enter your expected annual investment return (typically 6-8% for stock market).

Step 6: View Results
The calculator shows:

• Whether you've reached your coast number
• How much more you need to reach it (if applicable)
• Timeline to coast FI

If you're comparing related numbers, our Share Incentive Calculator covers a similar calculation in more detail. For background reading, see Investopedia.

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CoastFIRE Formula Explained

The core formula uses compound interest:

Coast Number = FI Target ÷ (1 + Return Rate) ^ Years to Retirement

Example Calculation

• FI Target: $1,000,000
• Annual Return: 7%
• Years to Retirement: 25

Coast Number = $1,000,000 ÷ (1.07^25) = $1,000,000 ÷ 5.427 ≈ $184,290

With $184,290 invested today at 7% annual returns, you'll have ~$1,000,000 in 25 years.

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CoastFIRE vs. Traditional FIRE

Different strategies suit different goals:

Traditional FIRE
Accumulate your full FI number while working. Retire at any point (age 30s-40s typically). Requires high savings rate.

CoastFIRE
Accumulate a coast number earlier (mid-career), then work part-time or pursue lower-paying passion work. Retire at your target age (55-65).

Trade-offs

• CoastFIRE: Longer working career but more flexible mid-career options
• Traditional FIRE: Earlier complete retirement but requires extreme discipline

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Compound Interest and Coast Number

The power of coasting comes from exponential growth:

20-Year Coast Example

• $200,000 today at 7% return
• Grows to: $773,929 in 20 years (no additional contributions)

30-Year Coast Example

• Same $200,000 at 7% return
• Grows to: $1,513,069 in 30 years

The longer you coast, the larger the multiplier effect. A 25-year coasting period roughly 5-6x your coast number.

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Lifestyle Flexibility with CoastFIRE

Reaching coast FI creates unique flexibility:

Career Options After Coasting

• Reduce to part-time work (20 hours/week)
• Pursue lower-paying passion projects
• Take sabbaticals between jobs
• Switch to mission-driven work

You don't need to maximize income once coasted; your investments handle future retirement.

Lifestyle Design
CoastFIRE enables decades of lifestyle optimization before traditional retirement.

Many readers using this tool also check out the Law School Admissions Calculator for a related use case. You can also reference IRS.gov for official guidance on this topic.

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Tax Considerations for CoastFIRE

CoastFIRE taxation depends on account types:

Tax-Advantaged Accounts (401k, IRA, Roth)
Money grows tax-deferred or tax-free. Withdrawals in retirement are taxed (or not, for Roth).

Taxable Brokerage Accounts
Capital gains taxes apply annually on dividends/gains. Reduces effective return ~1-2% depending on tax rate.

Optimize your coast number calculation by accounting for your tax situation.

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Common CoastFIRE Calculator Mistakes

Mistake 1: Using Unrealistic Return Estimates
7-10% annual returns assume stock market performance. Bonds yield 3-4%. Use realistic average for your allocation.

Mistake 2: Forgetting Inflation
A $1M FI target in today's dollars won't have the same purchasing power in 30 years. Adjust your target upward for inflation (~2-3% annually).

Mistake 3: Not Accounting for Taxes
Estimated returns are usually pre-tax. Taxable accounts reduce effective return by ~1-2%.

Mistake 4: Changing Assumptions Mid-Coast
Market volatility happens. Even if your investments underperform initially, coasting still works long-term if you stay invested.

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FAQ: CoastFIRE Calculator

How accurate is the coast number calculation?
Very accurate mathematically. The only variable is actual investment returns, which vary year-to-year. Use 30-year historical averages for best estimates. For a related calculation, see our No Vig Bet Calculator.

What if I reach my coast number early?
You can coast immediately or keep investing to reach traditional FIRE earlier. The choice is yours.

Can CoastFIRE work with lower return rates?
Yes, but you need a proportionally higher coast number. Lower returns mean compound growth is slower.

What if the market crashes after I start coasting?
Volatility is normal. A 25+ year coasting period weathers multiple market cycles. Historical data shows recovery and growth despite crashes.

Is CoastFIRE tax-efficient?
Depends on account types used. Tax-advantaged accounts (401k, IRA) are most efficient. Taxable accounts have annual tax drag. See NerdWallet for more authoritative detail.

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Calculate your CoastFIRE number with our free calculator at growsagardencalculators.com. Input your age, retirement target, and expected returns to determine your coast number and timeline.