A short reference for the vocabulary the rest of the help center assumes. If you bump into a term elsewhere that isn't here, send us a note.

Cycle

One run of the simulation against a specific stretch of history (for example 1871-1901 or 1932-1962). FIREproof aggregates results across every available cycle to compute summary statistics like success rate.

Success rate

The share of historical cycles in which the portfolio survived to the end of the plan without going to zero. A binary survival metric. It does not measure how close you came to running out or how much you finished with.

Withdrawal order

The default sequence the engine pulls money from when expenses exceed income: typically taxable accounts first, then tax-deferred, then Roth. Account-level overrides and bracket-fill rules can change this.

Bracket fill

A withdrawal strategy that pulls just enough from tax-deferred accounts to "fill" a target federal income tax bracket each year. Useful for evening out lifetime tax bills and creating Roth conversion headroom.

Cost basis

The amount you originally paid for an investment. When you sell from a taxable brokerage, the capital gain is sale price minus cost basis. The engine tracks per-asset cost basis through the ledger so it can compute capital-gains tax accurately.

Real dollars

Dollars adjusted for inflation, expressed in today's purchasing power. The opposite is "nominal dollars," which are the actual numbers a future-year statement would show. FIREproof can display either.

Glide path

A target asset allocation that changes over time. For example moving from 80/20 stocks/bonds today to 50/50 by retirement. The engine rebalances each year toward the current point on the glide path.

Rebalancing

Adjusting holdings at year-end so the portfolio matches the target allocation. The engine rebalances after returns each simulated year.

Adjustment

Any timed change to the portfolio: an income flow (Job, Social Security, Pension), an expense (Healthcare, Education, one-time), a Roth Conversion, or a Real Estate event. Adjustments have a timeline and can be recurring or one-time.

Asset allocation

The share of a portfolio held in each asset class. Typically stocks, bonds, cash, and any custom assets you define. Set per account; rolled up to the portfolio level for rebalancing.

ACA cliff

A discontinuity in the Affordable Care Act premium subsidy. Earning one dollar more than a threshold can erase thousands of dollars in subsidy. The engine flags this in Plan Diagnostics.

IRMAA

Income-Related Monthly Adjustment Amount. The Medicare premium surcharge that kicks in at higher modified AGI. Avoiding the next IRMAA tier is a common goal for Roth conversion sizing.

Roth conversion

Moving money from a tax-deferred account (401k, Traditional IRA) into a Roth account, paying ordinary income tax on the converted amount today in exchange for tax-free growth and withdrawals later.

Sequence-of-returns risk

The risk that poor returns early in retirement permanently impair the portfolio, even if long-run average returns are fine. FIREproof's historical-cycle approach makes this visible because each cycle has its own ordering.

VPW

Variable Percentage Withdrawal. A spending rule that scales each year's withdrawal to the current portfolio balance and the household's age, so spending rises and falls with the market.

CAPE

Cyclically Adjusted Price-to-Earnings ratio. CAPE-based spending rules dial spending down when valuations are high (and forward returns are likely lower).

Guyton-Klinger

A guardrails-style spending rule with explicit floor and ceiling triggers. Spending grows with inflation in normal years but is cut after a poor market and increased after a good one.