Free Compound Interest Calculator
Enter a starting amount, monthly contribution, interest rate and time period to see how compound interest grows your money. The earlier you start, the more dramatic the result.
Compound Interest Calculator
Mr B says: The earlier you start, the less you need to contribute. Time is doing most of the work — a dollar invested at 25 is worth dramatically more than a dollar invested at 45.$
$
%
Compound growth summary
Total contributed—
Interest earned—
Final balance—
⚠️ This tool is for general guidance only and is not financial advice. Investment returns are not guaranteed.
Common questions
Compound interest questions
Compound interest means you earn interest on both your original deposit and on the interest you have already earned. Over time this creates exponential rather than linear growth — the longer the time period, the more dramatic the effect. It is often called the most powerful force in personal finance.
This calculator compounds monthly, which is the most common frequency for savings accounts and investment products. Some accounts compound daily (slightly better) and some annually (slightly worse). The difference between daily and monthly compounding is small over most time periods.
For illustrative purposes, 5–7% per year is a common assumption for diversified equity investments over the long term. Cash savings rates are lower and vary by provider and economic conditions. Use a conservative rate rather than an optimistic one for planning purposes — it is better to be pleasantly surprised than disappointed.
Yes, and much more aggressively on debt. A 20% APR credit card compounds against you just as powerfully as a 7% investment grows for you. This is why paying off high-interest debt first is so important — there is no investment that reliably returns 20% per year after tax.