Project how an investment grows with regular monthly contributions. Results update as you type.
Projected balance
$0
Compound interest means you earn returns on your returns. In year one, only your original money grows. In year two, the original money plus year one's gains grow. Each year the base gets bigger, which is why the growth curve above bends upward instead of rising in a straight line.
FV = P × (1 + r/n)n×t + PMT × [((1 + r/n)n×t − 1) ÷ (r/n)]
Where P is your starting amount, r is the annual rate, n is compounding periods per year, t is years, and PMT is your contribution per period. This calculator applies your monthly contribution at the end of each compounding period.
Doubling your timeline more than doubles your ending interest, because the steepest part of the curve comes last. Starting ten years earlier routinely beats contributing twice as much later.
A fixed monthly contribution is the quiet engine of most real-world portfolios. In the default example above, contributions make up a large share of the final balance in the early decades — then interest overtakes them.
Interest earned on both your original principal and previously earned interest. Over long periods this makes growth accelerate rather than stay linear.
More frequent compounding grows slightly faster at the same stated rate, but the difference between monthly and daily is small. Rate and time matter far more.
Broad stock market returns have historically averaged roughly 7–10% per year before inflation, but that's not guaranteed. Many planners model a conservative 6–7% for long horizons.