Compound interest is the engine behind long-term wealth: you earn returns not just on your original money but on all the returns it has already generated. Einstein reputedly called it the eighth wonder of the world — whether he did or not, the math genuinely is remarkable, and this calculator lets you see it working on your own numbers.
Como funciona
Enter your starting amount, the annual rate, how many times per year interest compounds (12 for monthly, 4 for quarterly, 1 for yearly), and the number of years. The calculator applies the compound growth formula and shows both the future value and how much of it is pure earned interest.
A fórmula
FV is the future value, P is the starting principal, r is the annual rate as a decimal, m is the number of compounding periods per year, and t is the time in years.
Exemplo resolvido
10,000 at 6% compounded monthly for 10 years: FV = 10,000 × (1 + 0.06/12)^120 ≈ 18,194. You earned 8,194 without adding a single extra unit — and the same deposit left for 20 years grows to about 33,102, because compounding accelerates with time.
Perguntas frequentes
Does compounding frequency really matter?
It matters, but less than people expect. Moving from annual to monthly compounding on 6% adds roughly 0.17 percentage points of effective yield. Time and rate matter far more than frequency.
What is the Rule of 72?
A quick mental shortcut: divide 72 by the annual rate to estimate how many years your money needs to double. At 6%, that's about 12 years; at 9%, about 8 years.
How is this different from simple interest?
Simple interest pays only on the original principal every period, so growth is linear. Compound interest pays on principal plus accumulated interest, so growth curves upward — the gap widens dramatically over long periods.