Compound Interest Calculator
Estimate how an opening balance and ongoing contributions could grow when interest is added to the balance and earns further interest.
FREE ONLINE CALCULATOR
Compound Interest Calculator
Change the settings below to calculate your result. You can check the assumptions further down this page.
Ending balance = opening balance × (1 + annual rate / compounding periods) ^ (years × compounding periods) when there are no further deposits.
How to use this compound interest calculator
We convert the stated nominal annual rate into an effective monthly rate for monthly contributions. You can enter zero as a contribution amount to model a single deposit. Each additional payment is assumed to occur at the end of its month.
Formula and calculation method
Ending balance = opening balance × (1 + annual rate / compounding periods) ^ (years × compounding periods) when there are no further deposits.
Worked example
Compare $5,000 at 5% nominal interest for five years with and without monthly additions. The extra deposits increase the amount contributed, while compounding determines the interest earned on each amount.
Understanding the result
The final balance combines money paid in and modeled interest. Read both figures: a large ending balance does not mean every dollar came from interest. With monthly deposits, each later contribution has fewer periods to earn interest than the opening amount.
When to use this calculator
When comparing savings options, keep the term, contribution schedule and starting balance identical. Change only the stated annual rate or compounding frequency to isolate its effect. Also check whether the bank quotes a nominal interest rate or APY, since those are not interchangeable.
What the results do not include
Rates remain constant in this model. Actual investment returns fluctuate; taxes, fees and inflation are not deducted.
Frequently asked questions
Does monthly compounding mean I deposit monthly?
No. Compounding controls how often interest is credited. Contributions are a separate setting.
Can the calculated return be guaranteed?
No. This is a mathematical projection based on your rate assumptions.
For education and estimates only. Check any contractual, tax, banking or employment terms that apply to your situation. The calculations are not financial advice or guaranteed returns.