What is the difference between compound and simple interest?

Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus any previously earned interest, so your interest earns interest over time. Over long periods or at high rates, the difference between the two becomes substantial.

What is the compound interest formula?

A = P(1 + r/n)^(nt). P is the principal (starting amount), r is the annual interest rate as a decimal, n is the number of compounding periods per year, and t is the number of years. A is the final balance including all interest.

How does compounding frequency affect growth?

More frequent compounding produces slightly higher returns. Daily compounding produces more than monthly, which produces more than quarterly, which produces more than annual. The difference is small at low rates but grows at higher rates and over longer periods.

Is my data sent to a server?

All calculations run locally in your browser using JavaScript. No data is sent to our servers at any point.

Compound interest calculator

Compound interest calculator is a finance tool that projects how an investment grows using A = P(1 + r/n)^(nt). It supports annual, quarterly, monthly, and daily compounding, displays a year-by-year breakdown, and separates total interest from principal. The tool runs in your browser.

Principal (starting amount)

Annual interest rate (%)

Compound frequency

Time period: 10 years

1 yr50 yrs

Formula: A = P(1 + r/n)^(nt) — where P = principal, r = annual rate, n = compounds/year, t = years

Dedicated pages

Frequency-specific compound interest calculators.

Compound interest formula calculator

Calculate compound interest using the formula A = P(1 + r/n)^(nt). See total interest and a year-by-year breakdown. Free, in-browser.

Daily compound interest calculator

Calculate daily compounding interest on any principal. See total interest and a year-by-year breakdown table. Free, runs in your browser.

Monthly compound interest calculator

Calculate monthly compounding interest on any principal. Includes final balance, total interest, and a year-by-year breakdown. Free, in-browser.

How to calculate compound interest

Enter the principal (starting amount).
Enter the annual interest rate as a percentage.
Choose how often interest compounds: annually, quarterly, monthly, or daily.
Set the time period with the slider. Your final amount and year-by-year table appear instantly.

Common uses

Projecting how a savings account or ISA balance grows over time with a fixed interest rate, working out the investment window with a date calculator
Comparing growth across different compounding frequencies to understand the effect of daily versus annual compounding
Combining with a percentage calculator to convert between rate formats before entering values

Technical specification

Algorithm or formula: Standard compound-interest formula A = P(1 + r/n)^(nt) where P is principal, r the annual rate as a decimal, n the compounding periods per year, and t the term in years.
Browser API or library: Pure JavaScript arithmetic and Math.pow. No external library.
Input limits: Any positive numeric principal, rate, and term. The year-by-year table is rendered for up to 50 years.
Output: Final balance, total interest earned, and a per-year table of balance growth.
Known limitations: No support for irregular deposits, withdrawals, inflation adjustment, or tax. Continuous compounding (Pe^(rt)) is not exposed.

Frequently asked questions

What is the difference between compound and simple interest?: Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus any previously earned interest, so your interest earns interest over time. Over long periods or at high rates, the difference between the two becomes substantial.
What is the compound interest formula?: A = P(1 + r/n)^(nt). P is the principal (starting amount), r is the annual interest rate as a decimal, n is the number of compounding periods per year, and t is the number of years. A is the final balance including all interest.
How does compounding frequency affect growth?: More frequent compounding produces slightly higher returns. Daily compounding produces more than monthly, which produces more than quarterly, which produces more than annual. The difference is small at low rates but grows at higher rates and over longer periods.
Is my data sent to a server?: All calculations run locally in your browser using JavaScript. No data is sent to our servers at any point.

Reviewed and tested May 25, 2026.