Money
Compound Interest Calculator
Enter a starting amount, interest rate and years to see your money grow with monthly compounding.
How it works
Future value = P(1 + r/12)^(12t) + monthly × [(1 + r/12)^(12t) − 1] ÷ (r/12), where P is principal, r is annual rate, and t is years. Monthly compounding matches most UK savings accounts. The result shows total value and how much of it is interest.
Frequently asked questions
What is compound interest?
Compound interest means you earn interest on your interest, not just the original principal. Over long periods, this creates exponential growth — Albert Einstein supposedly called it the eighth wonder of the world.
How does monthly compounding differ from annual?
Monthly compounding applies interest 12 times per year, giving you slightly more than the headline annual rate. The AER (Annual Equivalent Rate) on UK savings accounts already reflects this.