How this compound interest calculator works
The calculator converts the entered nominal annual rate and compounding frequency into an effective annual yield, then into a monthly-equivalent rate for the schedule. Contributions are applied at the beginning or end of their selected periods.
The U.S. Securities and Exchange Commission provides a similar compound interest planning tool using initial investment, contributions, time, rate and compounding frequency.
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Compound interest formula
P is principal, r is the nominal annual rate, m is compounding periods per year and t is years. Recurring contributions are added separately at their selected timing.
For goal-based deposit planning using APY, try the Savings Calculator. To compare borrowing costs, use the Loan Calculator.
Contribution timing and annual increases
A beginning-of-period contribution receives one more period of growth than an end-of-period contribution. An annual increase raises the recurring contribution once every 12 months, which can model a planned step-up in saving.
The schedule shows total contributed separately from estimated growth so the result is easier to audit.
Inflation-adjusted value
The real-value estimate discounts the future balance by the constant inflation assumption. It is a purchasing-power comparison, not a tax or investment-return calculation.
Important limitations
- Rates and returns are held constant.
- Taxes, account fees and transaction costs are not deducted.
- Contribution and compounding dates can differ at a real bank or investment provider.
- Market investments can lose value and do not earn a fixed return.
Worked example: Compound Interest
Enter the following values in the Compound Interest Calculator and calculate to reproduce this result. Dates below use year-month-day order. This is an illustrative scenario, not a personalized recommendation or a current quote.
- Initial balance: 10000
- Regular contribution: 0
- Length — years: 10
- Additional months: 0
- Estimated annual rate: 6
- Compounding frequency: Monthly
- Contribution frequency: Monthly
- Contribution timing: End of period
- Annual contribution increase: 0
- Annual inflation assumption: 0
- Projection start date: 2026-10-15
Example result: $18,194projected balance. The entered balance and contributions grow to an estimated $18,194 over 120 months.
How to interpret this example
The example distinguishes money contributed from modeled investment growth. Contribution timing and compounding frequency affect the balance. A fixed rate is an illustration, not a prediction of market returns; compare scenarios rather than treating one projection as certain.