Compound Interest Calculator
See how your money grows with compound interest over time.
What Is a Compound Interest Calculator?
Compound interest is interest earned on both your original money and on the interest that money has already earned. Unlike simple interest, which grows in a straight line, compounding creates a curve that bends upward over time — slowly at first, then faster and faster. A compound interest calculator shows you that curve in actual dollars, so you can see what a deposit or investment could become after years of growth at a given rate.
This effect is the engine behind long-term saving and investing. A retirement account, a high-yield savings account, and a child's college fund all rely on compounding to do the heavy lifting over decades. The three ingredients are the amount you start with, the rate of return, and time — and of the three, time is usually the most powerful, because growth in the later years builds on an ever-larger balance.
How to Use the Compound Interest Calculator
- Enter your principal — the starting amount you are putting in today.
- Enter the expected annual interest rate or rate of return as a percentage.
- Enter the number of years the money will stay invested, and pick how often interest compounds (yearly, quarterly, monthly, or daily).
- Click Calculate to see the future value of your money and how much of it came from interest.
The Compound Interest Formula
The calculator uses the standard formula A = P(1 + r/n)^(nt), where P is the principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is the number of years. More frequent compounding produces a slightly higher result, because interest starts earning its own interest sooner. The difference between monthly and daily compounding is small, but the difference between starting now and starting in ten years is enormous — that gap is the real lesson of the formula.
Tips for Growing Your Money
- Start as early as you can. Doubling your time horizon usually beats doubling your deposit.
- Remember that returns are not guaranteed in investments — use a conservative rate for planning, not a best-case one.
- Keep fees and taxes in mind: a 1% annual fee quietly compounds against you just as returns compound for you.
What is the difference between simple and compound interest?
Simple interest is paid only on the original principal, so the balance grows by the same amount each period. Compound interest is paid on the principal plus all previously earned interest, so the growth accelerates over time. Over long periods, the difference is very large.
How often should interest compound?
More frequent compounding always produces a slightly higher final amount, all else equal. Savings accounts commonly compound daily or monthly, while many investments are described with annual returns. The compounding frequency matters far less than the rate and the number of years.
What is the Rule of 72?
The Rule of 72 is a quick mental shortcut: divide 72 by your annual rate of return to estimate how many years it takes money to double. At 8%, money doubles in about 9 years; at 6%, about 12 years. It is an approximation, but a useful one.
Does this calculator account for inflation or taxes?
No. It shows nominal growth before taxes and inflation. To think in today's dollars, you can enter a rate reduced by expected inflation — for example, a 7% return with 3% inflation behaves roughly like a 4% real return.