How Find My FIRE Number Calculates FIRE Scenarios
The calculator is intentionally focused. It models a single portfolio in today's dollars, applies monthly compounding, and uses your annual spending to define the FIRE target.
Real Return
real return = (1 + nominal return) / (1 + inflation) - 1
This avoids mixing future inflated dollars with today's spending. A 7% nominal return and 2.5% inflation becomes a 4.39% real return.
Monthly Compounding
The real annual return is converted into a monthly rate. Each month, the current portfolio grows by that rate and then receives the monthly investment.
Coast FIRE
coast target today = FIRE number / (1 + real return) ^ years to target age
If your current portfolio is already above the coast target, the Coast FIRE gap is $0. If it is below, the gap is the extra invested balance needed today to stop contributing and still hit FI by the target age.
Model Limits
- Market returns are modeled as a steady average, not volatile yearly returns.
- Taxes, account type rules, and fees are not modeled.
- Withdrawal rates are planning assumptions, not guarantees.
- Results are educational and should be stress-tested before major decisions.