Free Compound Interest Calculator

What Is Compound Interest?

Compound interest is the process of earning interest on both your original principal and on previously accumulated interest. Unlike simple interest, which only applies to the initial amount, compound interest causes your savings or investment to grow exponentially over time. This is why Albert Einstein reportedly called compound interest the eighth wonder of the world.

For example, if you invest $10,000 at a 6% annual interest rate, you earn $600 in the first year. In the second year, you earn interest on $10,600 instead of just $10,000, yielding $636. This snowball effect accelerates dramatically over longer time horizons, which is why starting early is one of the most powerful financial decisions you can make.

How to Use This Compound Interest Calculator

1. 1

   Enter Your Initial Principal

   Type the starting amount you plan to invest or save. This is the lump sum that will begin earning compound interest immediately.

2. 2

   Set the Interest Rate and Compounding

   Enter the annual interest rate and choose how often interest compounds: annually, monthly, daily, or continuously. More frequent compounding yields slightly higher returns.

3. 3

   Add Optional Contributions

   Specify any regular deposits you plan to make monthly or annually. Choose whether contributions are made at the beginning or end of each period.

4. 4

   Click Calculate and Review Results

   View your future value, total interest earned, a breakdown pie chart, growth bar chart, and a detailed year-by-year or month-by-month accumulation schedule.

Compound Interest Formulas

The basic formula for compound interest is:

Where:

• P — principal amount (initial investment)
• A — future value after time t
• r — annual interest rate (decimal)
• n — number of compounding periods per year
• t — number of years

For continuous compounding, the formula becomes:

Where e is Euler's number, approximately 2.71828. Continuous compounding represents the theoretical maximum yield for a given nominal rate.

Understanding Compounding Frequencies

The frequency of compounding determines how often interest is calculated and added to your balance. Savings accounts and CDs typically compound daily or monthly. Mortgage loans and credit cards usually compound monthly. Our calculator supports nine frequencies: annually, semiannually, quarterly, monthly, semimonthly, biweekly, weekly, daily, and continuously.

For example, $10,000 at 6% for 10 years produces different results depending on compounding frequency: annually yields $17,908, monthly yields $18,194, daily yields $18,221, and continuously yields $18,221. While the differences may seem small, they compound significantly over longer time horizons and with larger principal amounts.

The Rule of 72

The Rule of 72 is a quick mental math shortcut to estimate how long it takes for money to double at a given interest rate. Simply divide 72 by the annual rate of return. At 6%, your money doubles in approximately 12 years. At 8%, it doubles in about 9 years. At 12%, it doubles in roughly 6 years. This rule works best for rates between 6% and 10%.

Why Use Our Compound Interest Calculator?