Compound interest calculator
Estimate future value and total interest for savings or investments using compound interest.
What is compound interest?
Compound interest means you earn interest on your original principal and on the interest you’ve already earned. This “interest on interest” effect is why compounding is powerful over long periods. The more frequently interest compounds (monthly vs yearly), the faster the balance can grow, assuming the same annual rate.
How to calculate compound interest
For a one-time deposit, the standard formula is: A = P × (1 + r/n)^(n×t). Here, P is principal, r is annual rate as a decimal (8% → 0.08), n is compounding frequency per year, and t is time in years. This calculator also supports optional contributions each period (for example, adding a fixed amount every month).
Compound interest formula
Final amount: A = P × (1 + r/n)^(n×t)
Total interest: A − P (ignoring contributions)
Why use this online compound interest calculator?
It helps you compare scenarios quickly: different rates, different time horizons, and different compounding frequencies. It’s useful for planning savings goals, evaluating investment growth assumptions, and understanding how long-term compounding changes outcomes even with small rate differences.