FIRE Number Calculator Formula

Understand the math behind the fire number calculator. Each variable explained with a worked example.

Use the FIRE Number Calculator

Formulas Used

FIRE Number

fire_number = annual_expenses / (withdrawal_rate / 100)

Progress

progress = current_savings / (annual_expenses / (withdrawal_rate / 100)) * 100

Remaining to Save

remaining = max(annual_expenses / (withdrawal_rate / 100) - current_savings, 0)

Variables

VariableDescriptionDefault
annual_expensesAnnual Expenses(USD)40000
withdrawal_rateSafe Withdrawal Rate(%)4
current_savingsCurrent Savings(USD)200000

How It Works

FIRE Number

FIRE Number = Annual Expenses / Withdrawal Rate

At a 4% withdrawal rate: FIRE Number = Annual Expenses x 25

Once your investment portfolio equals your FIRE number, you can theoretically live off the returns indefinitely.

FIRE Variants

| Type | Expenses | Multiplier | |---|---|---| | Lean FIRE | <$40k | x25 | | Regular FIRE | $40-80k | x25 | | Fat FIRE | >$80k | x25 |

Worked Example

$40,000 annual expenses, 4% withdrawal rate, $200,000 saved.

annual_expenses = 40000withdrawal_rate = 4current_savings = 200000
  1. 01FIRE number = $40,000 / 0.04 = $1,000,000
  2. 02Progress = $200,000 / $1,000,000 = 20%
  3. 03Remaining = $1,000,000 - $200,000 = $800,000

Ready to run the numbers?

Open FIRE Number Calculator