Know Your Number

What you need at retirement · and where you land

A few things about you

$

In today's dollars. A decent starting point is what you spend now × 0.8. Do not subtract Social Security here — there is a box for that below.

$

401(k), IRA, Roth, HSA, brokerage. Not the house.

$

Everything going in, yours and the employer match.

$

Household total, today's dollars. Leave it at 0 to ignore it.

The years before this are funded by the portfolio alone.

Your number at 51
$0

What you will have
$0
The gap
$0
How this is figured

The engine runs in today's dollars: your money grows at the rate of return minus inflation, which is the honest way to compare a dollar in 2050 with a dollar now. The Future dollars switch at the top of the results then restates every balance in the dollars of its own year, which is what a bank statement would say and what most calculators print. The plan underneath does not change, only the labels on it. Monthly amounts are left in today's money either way, because that is how you typed them in.

  • Your number is the balance at retirement that pays your spending every year until life expectancy and lands on zero — not a penny wasted, not a penny short. Social Security is subtracted from the years it actually arrives, not from every year.
  • Your current path grows what you have invested today, plus what you add each year, at the rate of return you set. Contributions are assumed to keep pace with inflation.
  • Money is withdrawn at the start of each retirement year, and what is left grows for the rest of that year.
  • The safe withdrawal rate shown on the Assumptions tab is only a cross-check. The number above comes from the year-by-year math, not from a rule of thumb.

What it does not do: taxes, one-time expenses, a paid-off mortgage, market crashes in the wrong order, or a spouse retiring on a different date. It is a straight line through a crooked world. Useful for aiming, not for promising.

Why other calculators give a bigger number

Run the same inputs through a withdrawal-rate calculator and it will quote you far more. Three things account for all of it, and none of them are mistakes on either side.

  • The dollars are different. Most tools take today's dollars in and hand future dollars back, so the years of inflation between now and retirement are baked into the headline. That is what the Future dollars switch does, and it is on by default here so the two line up.
  • They never spend the balance. Dividing spending by a withdrawal rate funds it forever and leaves the whole balance behind, while this page funds it to the age you set and lands on zero. Forever costs roughly a fifth more. Note that a withdrawal rate is a safety rule taken from market history, not a return forecast, so it is not comparable to the return boxes on the Assumptions tab. To price that plan properly, use the Leave it all ending instead of copying their rate.
  • Social Security. Most tools have no box for it and tell you to subtract the benefit from your monthly spending instead. Do that when you retire early and you have quietly credited yourself a check that will not arrive for fifteen years. Here it is a separate input that starts on the age you give it.

To reproduce another tool's answer: set its withdrawal rate in the box on the Assumptions tab, set Social Security to 0, switch the yearly investing to stays flat, and read the cross-check in future dollars.

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