What these tools do
They take assumptions you provide and project them forward using standard time-value-of-money arithmetic. The arithmetic is tested and, given the inputs, correct. That is the whole of what they do.
What they cannot do
They are not forecasts. A projection at 7% nominal does not predict 7%. It answers "what would happen if returns were exactly 7% every year", and no market has ever behaved that way. Real returns arrive unevenly, and the order they arrive in changes outcomes dramatically — which is the entire point of the 4% rule stress test.
These tools do not and cannot account for:
- actual market returns, volatility, or the sequence in which returns arrive;
- your tax position, filing status, state or country of residence;
- investment fees, fund expense ratios, trading costs or advisory fees;
- changes to contribution limits, withdrawal ages or tax law;
- your health, family circumstances, job security or risk tolerance;
- long-term care costs, disability, divorce or other major life events;
- currency risk if your assets and expenses are in different currencies.
Specific limitations by tool
Bridge Account Calculator
The 59½ threshold, Rule of 55, 72(t)/SEPP and Roth conversions are US-specific and do not apply elsewhere. Roth conversions are taxable events in the year they are made, with knock-on effects on ACA premium subsidies, capital gains brackets and state tax that this tool does not model. A 72(t) schedule broken early triggers retroactive penalties plus interest. Do not execute any of these without professional advice.
Barista FIRE Calculator
Assumes part-time income and health insurance costs remain constant in real terms. Neither is guaranteed: hours get cut, employers withdraw benefits, and premiums rise faster than general inflation and steeply with age. US marketplace subsidies depend on income in ways this tool does not model.
Die With Zero Calculator
Spending principal down to zero carries asymmetric risk: running out of money at 90 is far worse than dying with a surplus. Life expectancy is a median, so planning to zero at it implies roughly a coin-flip chance of outliving your money. The tool shows longevity bands for this reason. It does not model long-term care costs, which are the largest practical threat to a spend-down plan.
Coast FIRE Calculator
Entirely dependent on the assumed real return holding over decades, with no further contributions available to correct a shortfall. Modest differences in realised returns compound into large differences in outcome. Test conservative assumptions before relying on it.
4% Rule Stress Test
The return sequences are stylised illustrations, not historical data and not a backtest. They are hand-specified to demonstrate distinct shapes, and no external data is fetched. They show how sequence affects outcomes. They do not predict anything, and surviving all six scenarios does not mean a plan is safe.
The 4% rule is contested
It came from a study of a specific market history over a 30-year horizon. Whether it holds for a 50-year early retirement, at current valuations, in other countries, is genuinely disputed among people who have studied it carefully. We present it because it is the common reference point, not because it is settled.
Accuracy and corrections
The formulas are unit-tested against closed-form results, but errors are possible and rules change. If you find a mistake, please report it via the contact page. Corrections are acted on.
Affiliate disclosure
Some pages contain affiliate links inside clearly labelled recommendation blocks. If you open an account through one we may earn a commission at no extra cost to you. This never affects a calculator's output, and recommendation blocks are always visually separated from results.
Your responsibility
Decisions about when to retire, how much to withdraw and how to invest are among the most consequential financial decisions you will make, and they are irreversible in ways most decisions are not. Use these tools to understand the mechanics, then take professional advice before acting.