Interest Calculator
Work out simple and compound interest on any principal, rate and term, with a year-by-year schedule showing principal, interest and balance.
Updated September 2026 · Written and verified by Akash Pandey
Interest Calculator
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How to use the interest calculator
- Enter the principal, annual interest rate and term.
- Choose simple or compound interest, and for compound, how often interest is applied (yearly, monthly, quarterly, daily).
- Results show the total balance, interest earned and a year-by-year table you can copy.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest earns only on the original principal. Compound interest adds each period's interest to the balance, so later periods earn on previous interest - the classic "interest on interest".
What is the compound interest formula?
A = P × (1 + r/n)^(n×t), where P is principal, r the annual rate as a decimal, n the compounding frequency and t the term in years. The tool does this exactly.
How does compounding frequency matter?
The more often interest is applied, the more it grows at the same nominal rate - daily beats monthly, which beats yearly, though the gap narrows as the rate falls.
What is the rule of 72?
A rough shortcut: at a fixed annual rate r%, money doubles in about 72/r years. So at 6% it doubles roughly every 12 years.
Are results rounded?
Financial amounts are shown to two decimal places as in a bank statement; the underlying math keeps full precision.
Is the calculator private?
Yes - all math runs locally in your browser.
What is the mathematical difference between simple and compound interest?
Simple interest is earned only on the initial principal (P × r × t). Compound interest is earned on both the principal and previously accumulated interest.
How does compounding frequency (monthly vs annually) affect total returns?
More frequent compounding periods (e.g. monthly vs annually) yield slightly higher total returns because interest begins earning interest sooner.