How Rightmont Computes Your Financial Future

Most calculators apply one formula (like “25× your spending”). Rightmont instead simulates your finances one year at a time to any age: income and raises, contributions and employer match across every account (401(k), Roth 401(k), Traditional and Roth IRA, brokerage, HYSA, 529, UTMA), housing (mortgage amortization, property tax, insurance, appreciation), children, one-off major purchases, then taxes and spending, then retirement drawdown. The output is a year-by-year net worth path, a retirement-feasibility date, and lifetime taxes.

These are the defaults. You can override most of them for your own situation; when an example on the site uses a different number, it says so explicitly.

Your FIRE number is annual spending ÷ 4.0%, i.e. 25× what you spend in a year — a portfolio of $1,000,000 supports about $40,000 of annual withdrawals at the 4.0% rule. In retirement the engine draws down in tax-efficient order (cash, then brokerage, then pre-tax, then Roth), layers in Social Security and any pension, and reports the first year (if any) the plan runs short. The 4.0% rule is a planning baseline, not a guarantee — which is why we also run Monte Carlo (section 5).

Taxes are computed every year, not estimated once: progressive federal brackets on the $32,200 standard deduction (married filing jointly), a state rate (defaulting to 5.0%), FICA on wages, 15.0% long-term capital gains on brokerage withdrawals, and the IRS provisional-income rules for how much Social Security is taxable. Contribution limits (with catch-up) are enforced to the current IRS figures.

A single average return hides the biggest retirement risk: a bad market early in retirement. Rightmont runs many randomized return paths around the 7.0% average and reports the share that keep your plan funded — a probability of success, not a false promise. That is what separates a plan that survives a 2008-style start from one that only works on paper.

Being trustworthy means being clear about the edges. Rightmont does not currently model: sub-annual (monthly) detail, per-category inflation, health-shock or job-loss events (model these as a lower income or a one-off expense), AMT/NIIT or full state-specific brackets, dynamic “guardrail” withdrawal strategies in the base projection, or estate/gift tax. We would rather say so than imply a precision we don’t have.

Every number Rightmont publishes — on a plan, a scenario page, or in the chat — traces to this engine or to the constants above. Content is checked for arithmetic, framing, and claim accuracy before it ships, and re-checked over time. If a figure can’t be defended, we don’t publish it.