🔍 Compound Interest Calculator

PercentageCalculatorFree.com Team Last Updated: January 22, 2026

Calculate how your money grows with compound interest over time.

Initial Investment (Principal)

Annual Interest Rate (%)

Time Period (Years)

Compound Frequency

Final Amount

$0.00

Initial Investment:*

Total Interest Earned:*

Growth Percentage:*

How Compound Interest Works

What is Compound Interest?

Compound interest is "interest on interest" - you earn interest not only on your initial investment but also on the accumulated interest from previous periods. This creates exponential growth over time, often called the "eighth wonder of the world."

The Formula

Compound Interest Formula

A = P × (1 + r/n)^(n×t)

A= Final amount

P= Principal (initial investment)

r= Annual interest rate (decimal)

n= Compound frequency per year

t= Time in years

Step-by-Step Example

Problem: $1,000 invested at 6% compounded monthly for 10 years

Given: P=$1,000, r=6%=0.06, n=12, t=10

Step 1: A = 1000 × (1 + 0.06/12)^(12×10)

Step 2: A = 1000 × (1.005)^120

Step 3: A = 1000 × 1.8194 = $1,819.40

Answer: Final amount is $1,819.40, earning $819.40 in interest

Start Early: Time is your biggest ally with compound interest.
More Frequent = Better: Daily compounding beats annual compounding.
Rule of 72: Divide 72 by your interest rate to estimate years to double.

Einstein's Eighth Wonder

Compound interest is often called the eighth wonder of the world. It's interest earning interest, creating exponential growth over time. The key insight: time matters more than rate. Starting 10 years earlier often beats having a higher return rate.

The Rule of 72

Quick Calculation: Divide 72 by your interest rate to find doubling time
At 6%: Money doubles every 12 years (72 / 6 = 12)
At 8%: Money doubles every 9 years (72 / 8 = 9)

Compounding Frequency Matters

Daily compounding beats annual for the same nominal rate. At 10% nominal: Annual compounding yields 10.00%, monthly yields 10.47%, daily yields 10.52%. Over decades, these differences compound into substantial amounts. This is why APY (effective rate) is more meaningful than APR (nominal rate).

❓ Frequently Asked Questions

What is the difference between simple and compound interest?

Simple interest is calculated only on the principal. Compound interest is calculated on the principal plus any interest already earned ('interest on interest').

How does frequency of compounding affect the total?

The more frequently interest compounds (daily vs. annually), the more interest you earn because your balance grows faster.

What is the Rule of 72?

It's a shortcut to estimate how long it takes to double your money. Divide 72 by your annual interest rate (e.g., 72 / 6% = 12 years).

🔍 Authoritative References

For more information about advanced financial calculations, consult these trusted sources:

Investopedia - Financial education and investment guidance
SEC Investor Education - Official investor protection resources
Federal Reserve - Monetary policy and financial stability information