Deterministic FIRE projection
The headline FIRE number is annual retirement spending divided by the selected withdrawal rate. The projection converts the entered nominal return and inflation assumptions into a real return:
real return = (1 + nominal return) ÷ (1 + inflation) − 1Balances and contributions are projected in today’s dollars. Contributions stop at the estimated or selected retirement age. Results change immediately when an input changes.
Outside-super bridge
The bridge is the present value of annual spending between the retirement age and the entered preservation age, discounted using the same real return assumption. A retirement age is only marked viable when the projected total meets the FIRE number and the outside-super balance can cover that bridge.
Drawdown order
Annual spending is withdrawn at the beginning of each retirement year. The model uses outside-super assets first. Any remaining spending can come from super only once the entered preservation age is reached. The remaining balances then receive that year’s real return.
Retirement stress test
Each run generates 3,000 trials for each of three scenarios and combines them using visible scenario weights:
- Random sequence, 60%: observed return blocks are resampled throughout retirement.
- Early downturn, 20%: the worst observed block is placed at the beginning of retirement.
- Late downturn, 20%: the worst observed block is placed near the end of the horizon.
When market history is available, the calculator uses dividend-adjusted SPY and AGG prices from Financial Modeling Prep as a US-dollar share-and-bond analogue. Monthly returns are aligned, weighted to the selected conservative, balanced, or growth mix, converted to real returns using the entered inflation rate, and block-resampled. The exact provider, assets, observation period, and any warning are shown with every result.
If usable history is unavailable, the calculator clearly labels an assumption fallback. That model uses the entered real return, 15% annual volatility by default, and five-year negative shocks for the early- and late-downturn cases. Both modes cap annual real returns between −70% and 70% and use a fixed seed so identical inputs remain reproducible. The revised withdrawal-rate result tests rates in 0.25 percentage-point steps against the selected success target.
Important limitations
- Historical analogue paths are resampled scenarios, not forecasts or a replay of the assets you personally hold.
- The SPY/AGG analogue is US-dollar based and does not capture Australian tax, franking credits, currency hedging, or every asset class.
- The FIRE calculator does not model tax, fees, Age Pension eligibility, contribution caps, insurance, or changes in legislation.
- Preservation age is a user-entered planning assumption, not an eligibility determination.
- Success means the model funded the entered spending through age 100; it does not measure lifestyle suitability or advice appropriateness.
- All results are educational estimates and can differ materially from real outcomes.
Rebalancing method
The rebalancing tool makes buy-only, whole-share suggestions. It directs available cash toward underweight holdings while respecting the entered minimum order size. It does not recommend selling, account for tax or brokerage, or decide whether any investment is suitable.