Compound Interest Engine
Determine the future value of your capital by analyzing the impact of time and compounding frequency on your principal.
Growth Parameters
How the Compound Interest Calculator Works
Compound interest is interest calculated on both your original principal and the interest that has already accumulated. Because each period's interest is added back to the balance before the next period is calculated, growth accelerates over time rather than staying flat, as it would with simple interest.
Formula
A = P × (1 + r/n)^(n×t)- A — final balance after compounding
- P — initial principal
- r — annual interest rate, as a decimal
- n — compounding periods per year
- t — number of years
The calculator applies this formula using the principal, rate, time horizon, and compounding frequency you enter. A higher compounding frequency (daily vs. annually) produces a slightly larger final balance for the same nominal rate, because interest starts earning its own interest sooner.
If you add a recurring monthly contribution, the tool also compounds each future contribution for the time remaining until the end of the term, so the final balance reflects both principal growth and new capital added along the way.
Worked Example: $10,000 at 7% for 20 years, compounded annually
- P = $10,000, r = 0.07, n = 1, t = 20
- A = 10,000 × (1 + 0.07/1)^(1×20) = 10,000 × 1.07^20
- 1.07^20 ≈ 3.8697
A ≈ $38,697 — more than 3.8× the original principal, with no additional contributions.
Frequently Asked Questions
How is compound interest different from simple interest?
Simple interest is calculated only on the original principal for the entire term. Compound interest is recalculated each period on the running balance (principal plus all interest earned so far), which is why it grows faster the longer money stays invested.
Does compounding frequency matter much?
It matters, but less than the rate or time horizon. Moving from annual to monthly compounding at a given rate typically adds a small amount to the final balance — the bigger levers are a higher rate and a longer time horizon.