Compound Interest Calculator 2026
See how your money grows with compound interest. Add monthly contributions and compare compounding frequencies side by side.
Compound interest formula: A = P(1 + r/n)^(nt). $10,000 at 7% compounded annually for 30 years grows to $76,123. With monthly compounding at the same rate, it grows to $76,123 — the difference from compounding frequency is minimal at moderate rates but significant at high rates over long periods.
The Power of Compound Interest
Compound interest means earning interest on your interest. Each period, your accumulated balance — not just the original principal — earns returns. Over decades, this creates exponential growth that simple interest cannot match.
Daily vs Monthly Compounding
The difference between daily and monthly compounding on $10,000 at 8% over 20 years: daily = $49,268, monthly = $49,268. The gap is less than $50 — compounding frequency matters far less than rate and time.
The Real Variable: Time
Starting 10 years earlier has a more powerful effect than increasing your return by 2%. $10,000 at 8% for 30 years = $100,627. For 40 years = $217,245. The last 10 years add more than the first 30 combined — that is compound interest at work.