Calculation details
Planning estimate only, not financial, tax, or legal advice. Verify assumptions and current rules before making decisions.
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Use this result
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What does this calculator estimate?
An APY calculator converts a nominal interest rate into the annual percentage yield with compounding. Enter the rate and compounding frequency to see the true yearly return.
- APY = (1 + r/n)^n − 1
- More compounding = higher APY
- APY is the real return to compare
Why APY matters
Banks advertise nominal rates, but compounding means you actually earn more — APY includes it. Comparing accounts by APY rather than the headline rate shows the true return, especially for high-yield savings and CDs.
Limitations to watch for
APY assumes interest stays in the account. Some accounts compound daily but pay monthly — the difference is tiny. APY is an annualized figure; holding periods shorter than a year earn proportionally less.
How to use it in practice
Compare savings accounts and CDs by APY. Estimate growth over time using the balance formula. Note that rates can change on variable accounts after the promotional period.
['Enter the nominal annual rate.', 'Choose the compounding frequency.', 'Read the APY and projected balance.']
APY vs. APR: the difference that costs you
APY includes compounding; APR does not. A savings account quoting 5 percent APY compounds the interest you earn; a loan quoting 5 percent APR typically quotes simple interest on the principal. The two are not comparable numbers, which is why banks advertise APY for deposits and APR for loans. The calculator converts between nominal rate and APY so you can compare offers honestly.
Compounding frequency in practice
Monthly compounding is the most common for savings accounts; daily compounding appears on high-yield accounts and credit cards. At 5 percent nominal, monthly compounding yields about 5.12 percent APY and daily about 5.13 percent — the difference is small on a single year but compounds over time and larger balances. The calculator lets you test each frequency.
How to compare savings offers
Compare APY, not the headline rate or the monthly interest shown on a statement. A 4.9 percent APY account beats a 5.1 percent APR account — the labels are different math. Also factor in minimum balances, fees, and whether the rate is promotional. The calculator standardizes the comparison.
How to compare loan offers
For loans, compare APR, which folds in fees, and check the compounding convention. A credit card at 22 percent APR compounds daily; an installment loan at 22 percent APR amortizes monthly. The effective cost differs. The calculator shows the effective annual rate for the numbers you enter, making the labels comparable.
The math behind the result
APY = (1 + r/n)^n − 1, where r is the nominal rate and n the compounding periods per year. The calculator applies this directly to your inputs, so a 5 percent rate compounded monthly produces (1 + 0.05/12)^12 − 1 ≈ 5.12 percent. No approximation, no hidden assumptions beyond the frequency you choose.
How this calculator works
Formula
APY = (1 + r ÷ n)^n − 1, where r is the nominal annual rate and n is compounding periods per year. Balance after t years = principal × (1 + r/n)^(n×t).
Worked example
A 5% nominal rate compounded monthly: APY = (1 + 0.05/12)^12 − 1 ≈ 5.12% — the actual yearly return.
Assumptions to verify
- Interest is compounded at the selected frequency.
- No withdrawals are made during the period.
- The rate stays constant.
Frequently asked questions
What is APY?
Annual percentage yield — the true yearly return including compounding. 5% compounded monthly = 5.12% APY.
How is APY calculated?
APY = (1 + r/n)^n − 1, where r is the nominal rate and n the compounding periods per year.
What's the difference between APR and APY?
APR is a borrowing rate (cost); APY is a deposit yield (return). APY includes compounding effects.
Why does compounding frequency matter?
More frequent compounding earns interest on interest sooner — daily beats monthly beats annually, though the gap narrows.
What's a good APY for savings?
High-yield savings accounts have offered 4–5%+ APY in recent cycles; traditional accounts pay far less. Rates move with the Fed.
How do I estimate growth?
Balance = principal × (1 + r/n)^(n×t). The tool shows this for your inputs.
Is the APY guaranteed?
Only for fixed-rate products (CDs lock the rate). Variable accounts can change APY after promotional periods.
What is the difference between APY and APR?
APY includes compounding (used for savings); APR is the simple quoted rate (common on loans). They are not directly comparable.
How often do banks compound interest?
Most savings accounts compound monthly; some high-yield accounts and credit cards compound daily.
Does compounding frequency really matter?
At the same nominal rate, more frequent compounding yields slightly more — monthly vs daily is a small but real difference over time.
What does 5% APY mean on a $10,000 deposit?
It means about $512 earned in the first year if interest compounds monthly — the rate already includes compounding.
Cite this tool
BoringToolsKit. “APY Calculator.” boringtoolskit.com/apy-calculator/ (reviewed 2026-08-25). Free to reference in articles, syllabi, and answer posts with a link.
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