Compound Interest Guide
How to Use a Compound Interest Calculator
A beginner-friendly guide to entering values, reading results, and understanding the limits of a compound interest estimate.
In this guide
Start with the money you already have Choose a realistic rate Read the output carefullyStart with the money you already have
The initial deposit is the amount you already have available to save or invest. This might be $500 in a savings account, $10,000 in a brokerage account, or any other starting amount.
If you do not have a starting balance, you can enter 0 and use the recurring contribution field to model future deposits.
Choose a realistic rate
The annual interest rate is your estimated yearly return. A bank savings account, bond fund, stock index fund, and retirement portfolio can all have very different expected returns and risk levels.
A calculator can show the math, but it cannot guarantee that a rate will happen. That is why the rate variance field is useful: it shows lower and higher outcomes around your base assumption.
Read the output carefully
Future value is the estimated ending balance. Total contributions show how much money you personally put in. Interest earned shows how much of the ending balance came from growth.
The year-by-year table is often more useful than the final number alone because it shows how growth changes over time.