Compound Interest Calculator
See how a starting balance plus regular contributions compounds monthly over time.
How it works
- 1
Enter your starting point
Your current balance and, if you'll be adding to it, a monthly contribution amount.
- 2
Set a growth rate and time horizon
An expected annual return and the number of years you plan to keep contributing and growing the balance.
- 3
Watch it compound
Interest is calculated monthly on the full balance — including previously earned interest — so growth accelerates the longer you leave it invested.
Frequently asked questions
What is compound interest?+
Compound interest is interest calculated on both your original balance and any interest that's already been added to it. Over time this creates exponential rather than linear growth — the longer your money compounds, the faster it grows.
What return rate is realistic?+
Historically, diversified stock market index funds have returned roughly 7–10% annually before inflation over long periods, though any individual year can vary widely. Savings accounts and bonds typically offer lower, steadier returns. Use a rate that matches your actual investment mix.
How often is interest compounded here?+
This calculator compounds monthly, meaning interest is calculated and added to your balance every month, which is standard for most savings and investment accounts.
Does this account for taxes or fees?+
No — the projection shown is gross growth before any taxes on investment gains or account/management fees, which would reduce your real-world return.