Notes on retirement maths
Plain-English notes on the retirement maths behind the free Retirement Scenario Modeler: RMDs, Social Security timing, sequence-of-returns risk, and what the projections actually assume.
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The RMD you didn't ask for isn't an investment decision
Required minimum distributions force money out of a 401(k) whether you need it or not. Most projections quietly reinvest the surplus at the market return. That one assumption can overstate late-life wealth by a third.
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The Rule of 55, and the three ways to lose it
A 401(k) can pay you at 55 with no early withdrawal penalty, four and a half years before the age everyone quotes. The exception attaches to one plan at one moment, and the most ordinary thing you can do with a 401(k) destroys it permanently.
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Your Coast FIRE number is lower than you think
The formula every Coast FIRE calculator uses assumes your portfolio pays for all of retirement. Most people's does not have to. What Social Security does to the number, and how to work it out properly.
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The ten years that beat thirty
The same $6,000 a year, started at 20, at 30 and at 40. What compounding does with the difference, and why ten years of saving in your twenties can finish ahead of thirty years of saving after.
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What this site is for
A free retirement calculator that answers one question: do I have enough to retire? What it models, who it is for, and what it deliberately leaves out.
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The gap year problem
When one partner retires years before the other, the household is neither fully working nor fully retired. Most calculators cannot express that, and the error runs in an optimistic direction.
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What the projection actually assumes
Every retirement calculator hides a pile of assumptions behind one number. Here are the ones this tool makes, stated plainly, so you can judge whether the answer applies to you.