Methodology

One plan, five steps, one engine

Each method is documented below with its inputs and outputs.

Start with the timeline

The timeline step records ages and the horizon: today, planned retirement, and optional spouse ages on one household axis. The net-worth step records present resources by asset class. Approximate figures are sufficient; a breakdown can be added wherever greater precision is wanted. Everything saves automatically on the device, so a change to expenses is reflected in the income, expenses, and spend-down steps together.

Each step answers one question

The order follows the U.S. Department of Labor's planning sequence: establish present resources, project lifetime income and expenses, then test how the balance pays out and whether the plan lasts. Each step hands its result to the next, and the dashboard turns the five answers into one verdict.

1 · Timeline

Today's age, planned retirement age, and optional spouse ages on one household axis. Everything else hangs off this line.

2 · Net worth

Assets in broad classes: cash, investments, retirement accounts, real estate, business, and other. Debts subtract from the total. The spendable pool funds the simulation.

3 · Lifetime income

Salaries with raises to each earner's retirement, Social Security auto-placed at the claim age, required withdrawals estimated from 73. One stacked lifetime chart.

4 · Lifetime expenses

A monthly headline or a category breakdown, an optional retiree smile curve, and the mortgage to payoff. Plotted against income; the crossover is where drawdown begins.

5 · Spend-down

Four ways to take money out, each tested on the same 500 runs with lifespans drawn. A verdict for each way, the best named, and the full working shown.

Under the hood

Deterministic timelines first

Income and expenses are projected year by year with no randomness. That covers salary growth, benefit claim ages, the smile curve, and mortgage amortization. Savings are computed from the same numbers instead of entered: salary and other inflows, minus expenses, minus tax, plus any extra you set. These timelines feed the income, crossover, and spend-down charts, and every row can be audited in the replay.

One projector, two market models

Every way runs the same year-by-year simulation. The pool grows by that year's market return, the gap is taken out by that way's rule, forced withdrawals are taxed once and any excess is reinvested, and fees and inflation apply. Modelled markets draw from a lognormal distribution; historical markets replay rolling windows from 1928 to 2024.

Mortality-weighted horizons

Each run draws lifespans from a simplified mortality table, and for couples the horizon ends at the second death. So running out of money is measured across runs, not assumed away with a fixed death date. The charts rank the runs still going at each age.

Two checks, then a verdict

Every way is scored on the same runs against two checks. How often the money still holds your target amount at your goal age, and how little the leanest year pays in the worst runs. A way works only when it passes both, and the plan lasts when at least one way does.

Single-lever fixes

When no way works, the dashboard suggests one change at a time: the earliest retirement age that works, the smallest increase in extra savings, or, for Steady, the highest sustainable rate. Each one names the way it unlocks.

Show your work

Every assumption is listed, three scenarios (bad-luck, median, good-luck) replay year by year with CSV export, failures are histogrammed by age, and a no-luck projection reconciles against the stochastic median as a standing self-check.

The four ways in detail: Steady takes the same amount every year, Flexible takes a share of the balance, Spend-all spends down to your target, and Guardrails trims and raises with the market. Compare them in our guide to withdrawal strategies.

What the charts mean

The chart shows the range of pool balances over time. Half of all runs land inside the band. The center line is the middle run, and the outer lines are the unlucky and lucky market sequences. Because lifespans differ, the bands thin toward the right, since late ages count only the runs still going. When the low line hits zero early, about one run in ten has run out of money. The fixes are to save more, spend less, retire later, or build in more flexibility.

Privacy and your data

The plan is stored only in the browser (local storage on the device). There are no accounts and no servers holding plan data.
All simulations run locally on the device. Financial inputs are not transmitted elsewhere for computation.
Anonymous usage analytics (for example, which modules are opened) are collected for product improvement. Financial values do not leave the browser.
Clearing the browser's site data erases the plan. Export anything important before switching devices.

This is an educational modelling tool, not financial advice. Results depend on the stated assumptions and do not guarantee future outcomes. Consult a qualified advisor before making decisions.