What to select
Enter a starting balance, annual rate, investment period and optional monthly contribution.
Compound Interest Calculator
Estimate investment growth from a starting balance, monthly contributions and compound interest.
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How this calculator works
Estimate how a starting balance and regular monthly deposits may grow when interest is added to the balance each month.
The calculator compounds the starting balance monthly and treats each monthly contribution as an end-of-month deposit. It also separates money contributed from estimated interest earned.
Formula
FV = P(1 + r)ⁿ + PMT × [((1 + r)ⁿ − 1) ÷ r]
Example
A starting balance of 10,000 at 5% a year with 500 added monthly for 10 years grows to approximately 94,111. Interest contributes approximately 24,111 of that total.
Important: This is an educational projection. It does not include fees, taxes, changing rates, inflation or investment losses.
Supported formats
Arithmetic expressions, percentages, powers, square roots, numbers, calendar dates, clock times and common measurement units.
Limits and safety
Standard calculations are limited to 256 characters. Results use JavaScript floating-point arithmetic; verify financial, legal or time-sensitive decisions independently.
Frequently asked questions
Are my calculation values saved?
No. Calculator inputs and results stay in this browser tab.
Can I rely on these results professionally?
Use them as general estimates. Lenders, billing systems, calendars and rounding rules may produce different results.