Calculation methodology

FIRE target equals annual spending divided by a withdrawal-rate assumption. Monthly spending is annualized by multiplying by 12. Gap and surplus are separately bounded at zero. Withdrawal-rate scenarios apply five fixed rates without calling any one rate safe.

Projection calculators convert effective annual return and inflation assumptions into decimal monthly factors. Beginning contributions are added before growth; end contributions are added afterwards. Annual contributions occur on explicit annual boundaries and are never silently divided into monthly payments. Real balances divide nominal balances by cumulative inflation.

FIRE date searches for the first month the portfolio meets an inflation-adjusted target. Coast FIRE discounts that future target using exact nominal growth relative to inflation and assumes no future deposits. Emergency fund uses expenses multiplied by coverage months; runway divides liquid funds by a positive monthly shortfall.

Inputs are bounded, calculations preserve supported decimal precision without monthly cent rounding, and displays use midpoint-to-even rounding. Deterministic projections are scenarios, not forecasts: taxes, pensions, allocation changes, volatility, and sequence-of-return risk are outside version 1.

Budgeting and wealth rules of thumb

The 50/30/20 budget splits after-tax income for the chosen period into 50% needs, 30% wants and 20% savings or extra debt payments. These categories are a planning framework, not mandatory spending amounts.

The Millionaire Next Door benchmark is age multiplied by annual pre-tax household income and divided by ten. Half and double the benchmark define the historical UAW and PAW thresholds. Zero income is left unclassified; this historical shortcut can be misleading early in a career.

The Rule of 72 displays approximate doubling years as 72 divided by annual return in percentage points. It is not an exact compounding calculation or forecast. Zero or negative steady returns do not double a positive balance.

Age-based allocation compares 100, 110 and 120 minus age. Shares are bounded to 0–100%, with the rest shown as bonds or cash. Age alone does not establish an appropriate portfolio.

The wealth ladder uses the original six USD bands with lower boundaries of 10,000, 100,000, 1 million, 10 million and 100 million. For positive net worth, the occasional-spending threshold is net worth divided by 10,000 and the earning-opportunity threshold is net worth divided by 100. Optional comparisons use unrounded values. Zero or negative net worth has no useful percentage verdict. These thresholds do not establish affordability or predict gains. Each calculator page links to background sources and explains its limits.