Methodology
How we model these projections.
Every Rionux calculator is a deterministic educational model, not a forecast. This page documents the assumptions behind our tools, the safeguards that keep results honest, and what we intentionally do not model.
Principles
Rionux calculators are educational models, not forecasts. They run entirely in your browser from the assumptions you enter, use no live market data, and are deterministic — identical inputs always produce identical results. Every output is shown under your assumptions.
How we model growth
Most projections use monthly compounding: an annual return assumption is converted to an equivalent monthly geometric rate and applied period by period, with contributions added on the same schedule. This mirrors how regular, long-term investing actually accumulates. Each calculator's own "How this works" section states the specifics for that tool.
How we handle inflation
Where a tool reports inflation-adjusted ("real", "today's dollars") figures, future values are discounted by the inflation rate you enter, so you can compare nominal growth against real purchasing power. Nominal and real values are shown side by side rather than blended.
Accuracy safeguards
All inputs are bounded and clamped, ratios are computed safely (a zero or invalid denominator yields zero, never an error), and results are finite-guarded so a calculator can never display NaN, Infinity, or a broken value. These guarantees are covered by automated tests.
What we intentionally do not model
To stay simple and honest, the calculators generally do not model fees, taxes, market volatility, or sequence-of-returns risk unless a specific tool says otherwise (some tools add explicit caveats, e.g. the FIRE tool's sequence-risk note). Real markets are variable; these tools show the shape of an assumption, not a promise.
Sources
Concepts follow standard, widely accepted financial definitions (e.g. compound interest, CAGR, real vs. nominal return, dollar-cost averaging). Where a term needs a precise definition, see the glossary; each guide also links to the concepts it builds on.