Coast Fire Calculator

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Coast FIRE Calculator

Your Coast FIRE Results

Coast FIRE Number
Amount needed today to reach your goal without further saving.
Target FIRE Number
The portfolio size you need at your retirement age (inflation-adjusted).
function calculateCoastFire() { var currentAge = parseFloat(document.getElementById('currentAge').value); var retirementAge = parseFloat(document.getElementById('retirementAge').value); var currentAssets = parseFloat(document.getElementById('currentAssets').value); var annualExpenses = parseFloat(document.getElementById('annualExpenses').value); var returnRate = parseFloat(document.getElementById('returnRate').value) / 100; var inflationRate = parseFloat(document.getElementById('inflationRate').value) / 100; var withdrawalRate = parseFloat(document.getElementById('withdrawalRate').value) / 100; if (isNaN(currentAge) || isNaN(retirementAge) || isNaN(currentAssets) || isNaN(annualExpenses)) { alert("Please enter valid numbers in all fields."); return; } if (retirementAge = coastFireNumber) { summaryText = "Congratulations! You have reached Coast FIRE. If you never save another penny, your investments should grow to support your retirement at age " + retirementAge + "."; } else { var gap = coastFireNumber – currentAssets; summaryText = "You are $" + gap.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 0}) + " away from reaching Coast FIRE. Keep investing to hit your milestone!"; } document.getElementById('resultSummary').innerHTML = summaryText; }

What is Coast FIRE?

Coast FIRE is a financial milestone where you have already saved enough in your retirement accounts that, even if you never contributed another dollar, your portfolio would grow through the power of compounding to provide a comfortable retirement by your target age.

Unlike traditional FIRE (Financial Independence, Retire Early), which requires a portfolio large enough to live off today, Coast FIRE simply means you no longer need to save for the future. You still need to work to cover your current living expenses, but you can "coast" into retirement by taking a lower-paying, less stressful job or spending more of your income now.

How to Use the Coast FIRE Calculator

To get an accurate result, you need to input several key variables based on your personal financial goals:

  • Current Age & Retirement Age: These determine the "time horizon" your money has to grow.
  • Current Invested Assets: The total value of your 401k, IRA, brokerage accounts, and other long-term investments.
  • Annual Expenses: Estimate what you will spend annually in retirement using today's dollar values. The calculator adjusts this for inflation.
  • Investment Return Rate: The annual percentage growth you expect from your portfolio. A common benchmark for a diversified stock portfolio is 7% after adjusting for some risks.
  • Safe Withdrawal Rate: Usually 4% (the "4% rule"), which represents the percentage of your portfolio you can withdraw annually without running out of money.

Coast FIRE Formula Logic

The calculation follows three primary steps:

  1. Future Target Expense: We calculate how much your current annual expenses will cost in the future due to inflation.
  2. Full FIRE Number: We divide those future expenses by your Safe Withdrawal Rate to find the total portfolio size needed at retirement.
  3. Present Value (Coast Number): We use the compound interest formula in reverse to determine what amount is needed today to reach that future goal based on your expected return rate.

Example Scenario

Imagine a 30-year-old with $100,000 invested. They want to retire at 65 and spend $50,000 a year. With a 7% expected return and 3% inflation, their future FIRE target at age 65 would be roughly $3.5 million. However, their "Coast FIRE" number today is only about $328,000. Since they only have $100,000, they aren't "coasting" yet, but they can see exactly how much more they need to invest to reach that freedom point.

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