Compound Interest Calculator
Calculate how your investments grow over time with compound interest. Compare daily, monthly, quarterly, and annual compounding with optional monthly contributions.
Additional amount added each month. Set to 0 for lump-sum only.
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Frequently asked questions
What is compound interest?
Compound interest means you earn interest on your accumulated interest, not just your original principal. Each compounding period, earned interest is added to your balance and the next period's calculation uses the larger number. Over long horizons this effect grows exponentially — a key reason why starting to invest early matters so much more than starting with a larger sum.
Does daily vs. monthly compounding make a big difference?
Less than most people expect. On $10,000 at 7% for 10 years, daily compounding yields about $5 more than monthly. The frequency matters far less than the rate and time horizon. Where compounding frequency really stings is on credit card debt — daily compounding at 24% APR adds up significantly over months. For savings and investments, focus on maximizing rate and time, not compounding frequency.
What is the Rule of 72?
Divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 6%, money doubles in roughly 12 years; at 9%, about 8 years. The rule is most accurate for rates between 5% and 15%. For an exact answer, the doubling time formula is ln(2) ÷ ln(1 + r) — but the Rule of 72 is close enough for quick mental math.