Compound Interest Calculator
Estimate how an initial balance and optional recurring contributions grow through compound interest with selectable compounding and contribution timing.
Formula
Without contributions: A = P(1 + r/n)^(nt). With contributions, future value is computed period-by-period using the selected compounding and contribution timing.
Assumptions
- Interest rate remains constant over the projection period unless you change inputs.
- Contributions occur at the selected frequency and timing throughout the duration.
- When compounding and contribution frequencies differ, growth is simulated month-by-month.
Limitations
- Projections only — not financial advice or guaranteed performance.
- Does not model taxes, fees, inflation, withdrawals, or changing rates.
- Negative rates are supported mathematically but may not reflect available products.
Worked example
$10,000 at 5% compounded monthly for 10 years
With no additional contributions, $10,000 at 5% compounded monthly grows to about $16,470 after 10 years. About $6,470 is interest earned.
Frequently asked questions
What is the difference between nominal and effective annual rate?
The nominal rate is the stated annual percentage. The effective annual rate (EAR) reflects compounding: EAR = (1 + r/n)^n − 1, where n is compounding periods per year.
When do beginning-of-period contributions earn interest?
Beginning-of-period contributions are added before interest accrues for that period, so they earn interest during the same period. End-of-period contributions are added after interest for that period.
Are these returns guaranteed?
No. Results are projections based on the rate you enter. Actual returns can change, and taxes, fees, inflation, and withdrawals are not modeled.
Last reviewed: 2026-07-22
Category: Finance
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