How This Retirement Calculator Works
Your savings grow two ways: the money you already have compounds, and each monthly contribution compounds from the month you make it. With monthly compounding, future value = current savings × (1 + r)n + monthly contribution × (((1 + r)n − 1) ÷ r), where r is the monthly return (annual return ÷ 12) and n is the number of months until retirement.
FV = P × (1 + r)n + PMT × (((1 + r)n − 1) ÷ r)r = annual return ÷ 12, n = months to retirement. Today's-dollar value = FV ÷ (1 + inflation)years.
Worked example: age 35 to 65 (30 years), $10,000 saved today, $500 a month, 7% annual return. Future value = $691,150.47. You put in $190,000 ($10,000 + $500 × 360 months), so growth is $501,150.47. At 3% inflation that $691,150.47 is worth $284,744.84 in today's dollars — the number that actually tells you what kind of retirement it buys.
Practical tips
A $691,000 headline at 7% return over 30 years sounds large until inflation is applied. Always read the today's-dollar line before deciding whether your plan is enough.
At 5% instead of 7%, the same example ends near $517,000 instead of $691,000. Use a cautious return for planning, not the best year you remember.
In the example, contributions of $500 a month supply $180,000 of the $190,000 put in — and their compounding supplies most of the growth. Consistency matters more than timing the market.
Returns vary, inflation varies, and this tool ignores taxes, fees and Social Security. Treat it as a planning estimate, not a guarantee.