Principal ($)
Annual rate (%)
Time (years)
Compounding
Result
About compound interest
The formula
A = P(1 + r/n)^(nt) where P=principal, r=annual rate, n=compounds per year, t=time in years.
Rule of 72
Divide 72 by the interest rate to estimate years to double your money. At 8% → doubles in ~9 years.
Frequency matters
Monthly compounding yields slightly more than annual. The difference grows significantly over long periods.