Coast FIRE Calculator
Calculate your exact Coast FIRE milestone number to find out when your current investments will grow into a full retirement nest egg without needing another dollar of savings.
Choose Retirement Spending Target
1. Age & Investment Horizon
years
Your age today (between 18 and 80)
years
Age when you plan to draw from investments
2. Spending, Assets & Savings Rate
$
Expected annual living costs in today's purchasing power
$
Total in 401(k), IRA, stocks, and mutual funds (exclude primary home)
$
Amount currently saved per year to project when gap closes
%
Standard 4.0% rule (25x expenses) or conservative 3.5% (28.6x)
3. Investment Returns & Inflation
%
Historical nominal stock index return (typically 9% to 10%)
%
Long-term average inflation (effective real return: 7.0%)
Enter your age, retirement timeline, expenses, and invested assets above to see your exact Coast FIRE milestone number.
How to Use This Calculator
- Enter your ages: Input your current age and your desired retirement age to establish your investment compounding timeline.
- Define your lifestyle spending: Enter your expected annual expenses in retirement (in today's dollars) or click one of the preset tiers (Lean FIRE, Standard FIRE, or Fat FIRE).
- Input current portfolio and savings: Enter your current invested assets across 401(k), IRA, brokerage accounts, and mutual funds (exclude your primary home equity), along with your optional annual ongoing savings.
- Review your Coast FIRE verdict: Instantly see if you have reached Coast FIRE, your exact dollar surplus or shortfall, and the projected growth of your money with zero extra savings.
The Formula
The Coast FIRE formula calculates the present value needed today so that compound interest alone expands your current investments into your full retirement nest egg by your target retirement age:
Coast FIRE Number = Target Nest Egg / (1 + r)^t
Target Nest Egg = Annual Retirement Expenses / Safe Withdrawal Rate (SWR)
Target Nest Egg = Annual Retirement Expenses / Safe Withdrawal Rate (SWR)
Where the mathematical parameters represent:
- Target Nest Egg: The total capital required to fund retirement indefinitely. Based on the 4% Safe Withdrawal Rule (25x annual spending), an annual retirement expense of $60,000 requires a $1,500,000 nest egg ($60,000 ÷ 0.04).
- r (Real Annual Return): The expected annual portfolio growth rate minus inflation:
r = ((1 + Nominal Return) / (1 + Inflation)) - 1, or approximated as Nominal Return minus Inflation (e.g. 9.5% nominal minus 2.5% inflation = 7.0% real return). - t (Compounding Horizon): Total years between your current age and your target retirement age (
Retirement Age - Current Age). - Surplus or Shortfall:
Current Invested Assets - Coast FIRE Number. If positive, you are 100% coasting. If negative, it shows the remaining gap to bridge.
Example Scenario
Consider Alex, age 30, who earns a good income but wants the freedom to leave a high-pressure corporate job and work on independent creative projects without worrying about saving for old age:
- Current Age: 30
- Target Retirement Age: 65 (Compounding horizon t = 35 years)
- Desired Retirement Spending: $60,000 per year (Standard FIRE)
- Safe Withdrawal Rate: 4.0% (Target Nest Egg = $60,000 ÷ 0.04 = $1,500,000)
- Expected Investment Performance: 9.5% nominal return with 2.5% inflation (7.0% real return)
- Current Portfolio Balance: $150,000 invested in broad-market index funds
Step 1: Calculate the Compounding Factor:
Growth Multiplier = (1 + 0.07)^35 = 10.6766
Step 2: Calculate the Coast FIRE Number:
Coast FIRE Target = $1,500,000 / 10.6766 = $140,494.39
Verdict: Because Alex already has $150,000 invested, Alex is $9,505.61 ahead of target (106.8% reached). Alex has achieved Coast FIRE! Even if Alex never saves another dollar into retirement accounts and only earns enough from low-stress freelance work to pay monthly rent and groceries, the existing $150,000 portfolio is mathematically projected to compound to $1,601,487 by age 65.
Frequently Asked Questions
What is Coast FIRE?
Coast FIRE is a milestone in the Financial Independence, Retire Early (FIRE) movement where you have accumulated enough money invested today that, through compound growth alone, it will reach your retirement nest egg goal by your desired retirement age without requiring you to contribute another penny. At Coast FIRE, you only need to earn enough to cover your day-to-day living expenses.
How is the Coast FIRE number calculated?
Your Coast FIRE number is the present value of your target retirement nest egg. First, determine your total retirement target using the 25x Rule (Annual Expenses divided by your Safe Withdrawal Rate, typically 4%). Then, discount that target back to today using your expected real annual rate of return: Coast Number = Target Nest Egg / (1 + Real Return)^Years until Retirement.
What should I do once I reach Coast FIRE?
Once you reach Coast FIRE, you no longer have to save aggressively for retirement. You can downshift to a lower-stress career, work part-time, switch to freelancing, take a sabbatical, or spend more of your current income on travel, family, and hobbies, knowing that compound growth is already handling your future retirement.
What is the difference between Coast FIRE and Barista FIRE?
Coast FIRE means your investments remain untouched until traditional retirement age while you earn enough from work to cover 100% of your current lifestyle expenses. Barista FIRE means you semi-retire early, pulling small withdrawals from your portfolio while working a part-time job to cover remaining living costs or health insurance benefits.
What is a safe real rate of return to assume for Coast FIRE?
Most financial planners recommend using an inflation-adjusted real return between 5.0% and 7.0%. Historically, broad index funds like the S&P 500 have generated approximately 10% nominal annual returns and roughly 7% real returns after accounting for long-term inflation. Using a conservative 5.5% to 6.0% real return provides a comfortable safety buffer.