Interest earned
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Compound Interest Calculator — Final Amount & APY
See how a single deposit grows with compound interest. Pick how often the interest compounds — daily for crypto/stocks, monthly for HYSAs, quarterly for bonds.
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final amount
Growth multiple
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Effective APY
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More frequent compounding = slightly more interest, but the difference is small. The bigger factors are the interest rate and time horizon.
How compounding frequency matters
A 5% rate compounded daily yields 5.1267% APY; compounded monthly it is 5.116%; annually, 5.0%. The difference is small at low rates, but at 20% or higher, daily compounding can add 0.5-1% extra per year. For practical purposes, monthly is the right default for most savings accounts.
How this calculator works
Final = Principal × (1 + rate/n)^(n × years), where n is compounding periods per year. Effective APY = (1 + rate/n)^n - 1, the actual annual yield when compounding is more frequent than annual.
Frequently asked questions
What is the rule of 72?
A quick mental math: 72 / interest rate = years to double your money. At 7% (stock market average), your money doubles every ~10 years. At 4% (HYSA), it takes 18 years. At 2% (checking account), 36 years. The rule is exact for 8% and reasonably accurate for rates between 4-12%.
How often do real savings accounts compound?
Most US high-yield savings accounts (HYSAs) compound daily but credit interest monthly. So your balance accrues interest every day, but the actual deposit to your account happens once a month. CDs and bonds typically compound semi-annually. Stock dividends reinvest — for those, monthly or quarterly is a reasonable assumption.
Why does more frequent compounding only help a little?
Compounding is the magic of earning interest on your interest. But that "interest on interest" only happens on interest that has already been credited. The difference between daily and monthly compounding is just whether that credit happens 365 or 12 times a year — at low rates the gap is tiny because each credit is small. At higher rates, the gap widens.
Last updated — rates and figures change over time, so always confirm with the current source.
Estimates for general information only, not financial advice — see our disclaimer.