Compound Interest Calculator
Calculate future value, total contributions, and estimated interest earned from compound growth.
Growth over time
See how contributions and compound growth build the balance over the selected period.
How this calculator works
How to use this calculator
Enter your starting amount, monthly contribution, annual interest rate, and time period. Choose how often interest is compounded, then click Calculate Compound Interest.
Formula used
For a single starting amount, compound interest is commonly calculated as A = P(1 + r/n)^(nt), where P is the principal, r is the annual interest rate, n is the selected number of compounding periods per year, and t is time in years.
Because this calculator accepts monthly contributions, it converts the selected compounding frequency to an equivalent monthly growth rate:
Monthly growth rate = (1 + r/n)^(n/12) − 1
Each month, the current balance grows by that monthly rate and the monthly contribution is then added.
Example calculation
Example: $1,000 starting amount, $100 monthly contribution, 6% annual rate, 10 years, monthly compounding
Monthly rate = 6% ÷ 12 = 0.5%
After 120 monthly periods, with the $100 contribution added after each month's growth:
Estimated future value ≈ $18,207.33
Total contributions = $13,000
Estimated interest earned ≈ $5,207.33
What the result means
The future value is an estimate of how much your balance could grow if the rate, compounding frequency, and monthly contributions stay constant. Actual investment returns can change and are not guaranteed.
Frequently asked questions
Does the compounding frequency change the result?
Yes. The calculator uses the selected compounding frequency to derive the growth rate applied across the monthly contribution schedule.
When is the monthly contribution added?
The calculator adds each monthly contribution after that month's growth is applied.
Does this include taxes or fees?
No. This calculator does not include taxes, inflation, account fees, or investment risk.
Can the interest rate be negative?
Negative rates are allowed only when the selected compounding frequency still produces a mathematically valid compounding base.
Is this financial advice?
No. This is an educational estimate only.