Compound Interest Calculator — See How Your Money Grows
Calculate the future value of any investment with compound interest. Add a monthly contribution and choose how often interest compounds — annually, quarterly, monthly, or daily. See your total balance, interest earned, and growth multiple.
Compound interest is the most powerful force in personal finance. This calculator shows you exactly how your savings and investments grow over time.
Free foreverNo data storedInstant resultsAccurate formula
Investment details
Enter an amount and rate above to see your investment grow.
Investment growth
Final balance
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Total interest earned
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Total contributed
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Growth multiple
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Interest / year (avg)
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Years to double (Rule of 72)
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How Compound Interest Works
Simple interest pays you interest only on your original principal. Compound interest pays interest on your principal plus all previously earned interest — so your money grows exponentially rather than linearly. Albert Einstein reportedly called it "the eighth wonder of the world."
Formula: A = P × (1 + r/n)^(n×t) Where: P = principal · r = annual rate · n = compounds per year · t = years
Real example: $5,000 at 8% for 20 years (monthly compounding)
Final balance: $24,711 · Interest earned: $19,711 That's nearly 5× your original investment — with zero extra contributions.
The Rule of 72
A quick mental shortcut: divide 72 by the interest rate to estimate how many years it takes to double your money. At 8% annual return: 72 ÷ 8 = 9 years to double. At 6%: 12 years. At 10%: 7.2 years.
The frequency of compounding also matters. Daily compounding produces slightly more than monthly, which produces more than annual. Over long periods on large balances, this difference becomes meaningful.
Frequently Asked Questions
What is compound interest?
Compound interest means earning interest on both your original principal and your accumulated interest. Unlike simple interest (which only pays on the principal), compound interest grows exponentially over time — meaning money earns money on money.
How often should interest compound?
More frequent compounding means slightly higher returns. Daily compounding earns more than monthly, which earns more than annual. However, the difference between daily and monthly is very small. What matters most is the interest rate and how long you stay invested.
What is the Rule of 72?
The Rule of 72 is a mental shortcut to estimate how long it takes to double an investment. Divide 72 by the annual interest rate. Example: at 9% return, 72 ÷ 9 = 8 years to double. At 6%, it takes 12 years.
How do monthly contributions affect growth?
Regular contributions dramatically accelerate wealth building. Even small monthly amounts, when compounded over decades, create substantial wealth due to each contribution earning compound returns from the moment it is added. This is the principle behind pension contributions and regular investment plans.