Why results are shown in today's dollars
A million dollars 30 years from now won't buy what a million buys today. This calculator deflates your projected balance by your inflation assumption so the headline number answers the question you actually care about: how much purchasing power will I have? The smaller "nominal" figure shown underneath is what your statement balance would literally read.
The 4% rule, briefly
The 4% rule comes from research on how much a retiree could withdraw annually — adjusted for inflation each year — without exhausting a balanced portfolio over a 30-year retirement. It's a planning shorthand, not a guarantee: retiring into a market crash, living past 95, or holding a very conservative portfolio all argue for a lower rate, while pensions and flexibility argue you can be less strict.
The gap solver is the point
Most retirement calculators stop at a big scary number. This one solves the reverse problem: given your income goal and Social Security estimate, it computes the nest egg you'd need and the exact additional monthly contribution that gets you there by your chosen age. Small changes compound — starting five years earlier routinely cuts the required monthly amount by a third or more.
Choosing a return assumption
The 7% default approximates the long-run inflation-adjusted-plus-inflation return of a diversified stock-heavy portfolio; 5% suits bond-heavy allocations or conservative planners; 9% reflects an aggressive all-equity stance and optimistic markets. When in doubt, plan with the lower number — pleasant surprises are easier to handle than shortfalls.