Compound Interest Calculator
See exactly how your savings or investments grow over time. Add a starting balance and monthly contributions, choose your rate, and watch compounding do the heavy lifting.
Growth over time
Year-by-year breakdown
| Year | Contributions | Interest | Balance |
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How compound interest works
Compound interest is often called the eighth wonder of the world, and for good reason. Unlike simple interest — which only ever pays you on your original deposit — compound interest pays you on your deposit and on all the interest you've already earned. Each period, your balance is a little bigger, so the next round of interest is a little bigger too. Given enough time, that snowball becomes the majority of your wealth.
The formula
The classic compound interest formula is:
A = P × (1 + r / n)n × t
- A — the final amount
- P — the principal (your starting balance)
- r — the annual interest rate, as a decimal
- n — how many times interest compounds per year
- t — the number of years
When you add regular monthly contributions, this calculator simulates every month individually: it grows your current balance by the effective monthly rate, then adds your deposit. That's the most accurate way to model a real-world savings plan.
A quick example
Say you start with $1,000, add $200 every month, and earn 7% a year compounded monthly. After 20 years you'll have put in $49,000 of your own money — but your balance will be roughly $108,000. That extra ~$59,000 is pure compound interest, earned while you slept.
Frequently asked questions
What is compound interest?
Compound interest is the interest you earn on both your original money and on the interest that money has already earned. Because each period's interest is added to the balance, your money grows faster and faster over time — often described as 'interest on interest'.
What is the compound interest formula?
The basic formula is A = P(1 + r/n)^(nt), where A is the final amount, P is the principal (starting balance), r is the annual interest rate as a decimal, n is the number of times interest compounds per year, and t is the number of years. When you also add regular contributions, each deposit is grown by the same formula for the time it stays invested.
How often should interest compound?
The more frequently interest compounds, the more you earn. Daily compounding beats monthly, which beats annual — though for typical rates the difference between daily and monthly is small. This calculator lets you compare annual, semi-annual, quarterly, monthly and daily compounding.
Does this calculator include regular contributions?
Yes. Enter a monthly contribution and the calculator simulates each month: it grows your existing balance, then adds your deposit. This models a real savings or investment plan where you keep adding money over time.
Is my data private?
Completely. All calculations run in your browser. Nothing you type is sent to a server or stored anywhere.
CalcOrchard is an educational tool. Results are estimates based on the numbers you enter and assume a constant rate of return. Real investments fluctuate. This is not financial advice.