Interest basics
Simple Interest Calculator
Calculate simple interest on a starting principal, optional monthly additions, and compare it with monthly compounding.
Simple interestprincipal times rate
Ending balanceprincipal plus interest
Compound gapsimple vs compound
Simple interest earned
$0
Ending balance$0
Total principal added$0
After-tax interest$0
Compound interest difference$0
Enter principal, rate, and time to estimate simple interest.
Yearly interest table
| Year | Principal | Simple balance | Compound balance |
|---|
How this simple interest calculator works
The calculator applies simple interest to the original principal and each monthly addition based on how long that deposit remains in the account. Simple interest does not earn interest on prior interest.
The compound comparison uses monthly compounding with the same rate and deposits. Actual loan, savings, tax, and investment rules can differ from this simplified estimate.