FIRE Calculator

Financial Independence, Retire Early

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Understanding FIRE

What is FIRE?

FIRE stands for Financial Independence / Retire Early. It's a personal finance milestone where you've accumulated enough invested assets that the returns on those investments can cover your cost of living — indefinitely.

Once you reach FIRE, you have the freedom to spend your time however you like, without needing to work for income. You don't have to wait until conventional retirement age — by saving aggressively and investing wisely, many people reach financial independence decades earlier.

How to Calculate Your FIRE Number

Your FIRE number is the total amount of money you need to have invested so that the returns from your portfolio can cover your ongoing living expenses. It's based on two inputs: your expected annual spending in retirement and your Safe Withdrawal Rate (SWR).

FIRE Number=Annual SpendingSWR\text{FIRE Number} = \frac{\text{Annual Spending}}{\text{SWR}}

For example, if you expect to spend $40,000 per year in retirement and use a 4% SWR:

FIRE Number=$40,0000.04=$1,000,000\text{FIRE Number} = \frac{\$40{,}000}{0.04} = \$1{,}000{,}000

That means you'd need $1,000,000 invested to sustain $40,000 per year in withdrawals.

The Safe Withdrawal Rate (SWR)

The Safe Withdrawal Rate is the percentage of your portfolio you can withdraw each year without running out of money. The most widely cited figure is 4%, based on the Trinity Study, which found that a 4% withdrawal rate had a 100% success rate over a 30-year retirement horizon with a 50/50 mix of stocks and bonds.

For earlier retirees with longer time horizons, a more conservative SWR of 3% to 3.5% may be appropriate. A lower SWR means a larger FIRE number but greater confidence that your money will last.

Annual Withdrawal=Net Worth×SWR\text{Annual Withdrawal} = \text{Net Worth} \times \text{SWR}

The Math Behind the Calculator

At its core, this calculator uses the compound interest formula to project your net worth over time:

A=P×(1+r)tA = P \times (1 + r)^t

Where A is the final amount, P is the principal (starting amount), r is the annual growth rate, and t is the time in years.

Your net worth is calculated year by year, building on the previous year's balance:

Wt=Wt−1×(1+rreal)+CW_{t} = W_{t-1} \times (1 + r_{\text{real}}) + C

Where:

  • W = net worth at each year
  • r_real = investment return minus inflation (the real rate of return)
  • C = annual contributions (take-home pay minus spending)

The simulation runs from your current age until you reach your FIRE number, showing you exactly when financial independence is expected.

What About Inflation?

Inflation is critical to account for when planning decades ahead. A dollar today won't have the same purchasing power 20 or 30 years from now. This calculator handles inflation by subtracting the expected inflation rate from your investment return to get a real (inflation-adjusted) rate of return:

rreal=rnominal−rinflationr_{\text{real}} = r_{\text{nominal}} - r_{\text{inflation}}

For example, with a 7% nominal return and 3% inflation:

rreal=7%−3%=4%r_{\text{real}} = 7\% - 3\% = 4\%

This means all the numbers in the calculator are expressed in today's dollars. Your FIRE number represents real purchasing power, not a future inflated figure. You don't have to worry about rising costs — it's already built in.

Assets like stocks and real estate tend to rise with inflation, while cash loses value. This is why having your money invested — rather than sitting in a savings account — is especially important for long-term wealth preservation.

Using This Calculator

Fill in the inputs at the top and the graph will show your projected path to FIRE. Here's what each field means:

  • Current Age — your age today, which sets the starting point for the projection
  • Retirement Age — the age you'd like to retire by (the calculator will tell you if you can reach FIRE sooner)
  • Current Net Worth — your total invested assets including stocks, bonds, cash, and retirement accounts (exclude real estate unless you plan to sell it in retirement)
  • Monthly Contributions — how much you save and invest each month
  • Investment Rate of Return — the average annual return you expect from your investments (default is 7%, which is conservative; the S&P 500 has historically returned about 10% annually)
  • Inflation Rate — the expected annual rate of inflation (U.S. historical average is about 3%)
  • Safe Withdrawal Rate — the percentage you plan to withdraw each year in retirement (4% is the most common recommendation)

Retirement Spending

Your annual spending in retirement is one of the most important inputs in the FIRE equation — it directly determines your FIRE number. In many cases, retirement spending will be lower than your current spending because:

  • You may have paid off your mortgage
  • You'll no longer be commuting or paying work-related expenses
  • Medicare may cover much of your healthcare
  • You won't be saving for retirement anymore

However, some costs may increase — travel, hobbies, and healthcare premiums before Medicare kicks in. Use the expected expenses section to add specific costs and get a more personalized FIRE number.

The Power of Savings Rate

The single most important factor in how quickly you reach FIRE is your savings rate — the percentage of your take-home pay that you invest. A higher savings rate works in two ways: it increases your contributions and simultaneously reduces your required FIRE number (because you're learning to live on less).

Savings Rate=Take-Home Pay−Annual SpendingTake-Home Pay×100%\text{Savings Rate} = \frac{\text{Take-Home Pay} - \text{Annual Spending}}{\text{Take-Home Pay}} \times 100\%

Someone saving 10% of their income might need 40+ years to reach FIRE, while someone saving 50% could get there in about 17 years. The relationship is not linear — every additional percentage point you save has an outsized impact.