Compound Interest Calculator
Explore how a starting balance, monthly contributions, time, and an assumed return can affect a long-term growth scenario.
Estimated result
Enter your detailsResults are educational estimates and do not include every fee, tax, or contract term.
Free to use. No account required. Your entries stay in this browser.
Explore the result
Result visual
Scenario comparison
How this compound interest calculator works
Formula used
The starting balance grows at an assumed monthly rate and each monthly contribution is added at the end of the period.
How to read the result
Run a range of return assumptions and time horizons. The gap between scenarios is more useful than treating one result as a forecast.
What the estimate leaves out
Actual returns are uneven and may be negative. The estimate can model a steady annual fee and inflation rate, but it still excludes taxes, trading costs, contribution changes, and return sequence.
Use the result as a starting point, then read how to learn how compounding, losses, and time interact. For formula details and test limits, see the calculator methodology.
Stress-test the growth assumption
A projection is more useful as a range than as a promise. Compare lower and higher return assumptions, then separate money contributed from modeled growth.
Subtract recurring fees
The tool approximates annual fees by reducing the assumed return. Real products may charge at different times or use flat and percentage fees together.
Look at purchasing power
The inflation-adjusted result estimates what the future balance may buy in today's dollars. It does not predict a specific future price.
Watch the contribution line
Early in many plans, deposits drive more of the balance than growth. A sustainable saving habit may matter more than a small change in the assumed return.
Use realistic inputs
Use a time horizon tied to the goal and a return range you can defend. Include ongoing fund or advisory fees and do not enter a past best year as a long-term expectation.
For the definitions and decisions behind these inputs, browse the investing basics learning path.
Verify terms before acting
Investing can lose value. Check product costs, taxes, account restrictions, asset risk, contribution timing, and whether the goal can tolerate a market decline near the deadline.