How the numbers become dates.

General modeling principles

Core finance tools are scenario models, not forecasts. They answer questions such as “what would happen if these assumptions held?” rather than claiming to know future market returns, inflation, spending, or life events.

Inputs should stay visible, defaults should be reasonable but editable, and advanced assumptions should be available without overwhelming the first interaction.

FIRE number

The FIRE-number calculation divides annual spending by the selected withdrawal-rate assumption. A 4% withdrawal rate is equivalent to roughly 25 times annual spending. This is a planning shortcut, not a guarantee that a portfolio will sustain every future retirement path.

Growth projections

Growth tools convert an annual return assumption into an equivalent periodic rate and project balances through time while applying recurring contributions according to the tool’s documented convention. Contributions and modeled investment growth are kept conceptually separate where the interface reports them.

Unless a tool explicitly says otherwise, these projections do not model taxes, trading costs, changing asset allocations, behavioral changes, or unexpected cash flows.

Milestone dates

When a projected balance crosses a target threshold, NumberCalendar converts that period into an estimated month or date. If the underlying model only has month-level precision, the interface should not imply exact-day certainty.

Retirement simulations

Retirement-income and withdrawal-strategy tools apply the assumptions shown in the interface to a selected horizon. The Monte Carlo simulator explores many reproducible return paths to show a distribution of outcomes rather than one average path.

A simulation success rate is not the probability that an individual user will succeed in real life. It is the percentage of simulated paths that met the model’s funding rule under the selected assumptions and distribution.

Calendar outputs

Financial calendars are presentation layers over the same underlying scenario and milestone engines. They should not silently recalculate a different target or invent a default scenario when the user has already supplied one.

Lottery statistics

Lottery frequency, gap, hot/cold, overdue, pair, sum, and related statistics describe historical records. For fair independent drawings, historical frequency does not make a valid future combination more or less likely merely because it was common, rare, or absent in the past.

Strategy backtests must avoid look-ahead bias: a historical strategy may only use information that would have been available before the draw being tested.

Model changes

When formulas or conventions change materially, the implementation and supporting methodology should be updated together. Important assumptions belong near the tool result as well as in this longer reference.

Methodology reviewed: September 8, 2026.