When a bank advertises a savings account at "4.50%", the number on the sign is almost always the nominal rate (APR), not the rate you actually earn after compounding. The number that really matters for depositors is the Annual Percentage Yield (APY) — the real, all-in return after interest has been compounded over a full year. This APY calculator converts a nominal rate into the effective annual yield, shows how much you will actually earn on your deposit, and lets you compare monthly, quarterly, daily, and annual compounding side by side.
Two savings accounts can both advertise 4.5% APR, yet one pays noticeably more than the other because it compounds daily instead of annually. Regulators in the United States require banks to display APY prominently on deposit products precisely so that shoppers can make an apples-to-apples comparison. Use this calculator before you lock in a CD, choose a high-yield savings account, or shop around between brokers.
How to Use
- Enter your Initial Deposit — the principal you are putting into the account today. If you only want to see the APY itself, any positive number works; the yield percentage is independent of the deposit size.
- Type the Nominal Interest Rate (APR) the bank is advertising. This is the headline rate, not the APY. Typical high-yield savings accounts in 2025–2026 sit between 3.5% and 5.0%; CDs range from about 4.0% to 5.5% depending on term.
- Pick the Compounding Frequency. Most savings accounts compound daily or monthly; CDs often compound monthly; bonds compound semiannually; the bank's fine print will tell you which.
- Set the Time Horizon in years. APY itself is always a one-year figure, but extending the horizon lets you see how compounding snowballs over a multi-year CD or a long savings runway.
- Read the result card. The highlighted APY is your true annual return; Future Value is what the deposit grows to; Total Interest is pure earnings.
Switch the compounding dropdown between Annual, Quarterly, Monthly, and Daily while leaving the rate untouched. The APY moves up each time you compound more often — that gap is the "free" extra return frequency gives you.
The APY Formula
The formula required by the US Truth in Savings Act (Regulation DD) is:
APY = (1 + r/n)ⁿ − 1
Where:
- r is the nominal annual rate in decimal form (so 5% becomes 0.05).
- n is the number of compounding periods in one year — 1 for annual, 4 for quarterly, 12 for monthly, 365 for daily.
The future value of a deposit after t years is:
FV = P × (1 + r/n)^(n·t)
Where P is the initial principal.
Worked example on a $10,000 deposit at a nominal 5.00% compounded monthly: the periodic rate is 0.05 / 12 = 0.004167, and APY = (1.004167)¹² − 1 = 5.116%. After one year the balance is $10,511.62 and you have earned $511.62 in interest. If that same 5.00% compounded only annually, the APY would be exactly 5.00% and you would earn $500.00 — so monthly compounding puts about $11.62 extra in your pocket for the year. On a $1,000,000 balance that same frequency choice is worth roughly $1,160 per year.
If the rate is 0%, the formula still holds: (1 + 0)ⁿ − 1 = 0, and the balance never grows.
Why Compounding Frequency Matters
Holding the nominal rate fixed, more frequent compounding always produces a higher APY, though the gains taper off as you move from monthly to daily:
- Annual (n=1): APY equals the nominal rate exactly.
- Quarterly (n=4): APY is about 0.06% higher than nominal on a 4% rate.
- Monthly (n=12): APY is about 0.09% higher.
- Daily (n=365): APY is about 0.10% higher.
The difference between monthly and daily compounding is small on a one-year horizon but becomes visible on larger balances and longer horizons. Banks know this, which is why "daily compounding" is a marketing line on high-yield savings products. Always compare APY, not APR, when shopping.
Examples
Example 1 — High-yield savings account. You deposit $10,000 at a 5.00% nominal rate compounded monthly. The APY is 5.12%, the balance after one year is $10,511.62, and you have earned $511.62 in interest. After five years at the same rate, the balance grows to about $12,834 — nearly $2,834 of pure compound interest on the original $10,000.
Example 2 — Quarterly-compounding CD. A bank offers a 12-month CD at 4.00% nominal, compounded quarterly. The APY is 4.06%, so a $5,000 deposit grows to $5,203.02 and earns $203.02. If a competing CD compounds the same 4.00% monthly, the APY rises to 4.07% — only about 50 cents more on $5,000, but meaningful on larger CDs.
Example 3 — Daily compounding on a large balance. A $1,000,000 portfolio earning a nominal 4.50% compounded monthly yields an APY of 4.59% and grows to $1,045,939.83 in one year, earning $45,939.83. Daily compounding on the same nominal rate pushes the APY to roughly 4.60% — about $100 of extra interest over the year, which is why treasury-only money-market funds advertise daily compounding.
Example 4 — Zero-rate boundary. If the nominal rate is 0%, the APY is exactly 0% and the future value equals the principal. This is not a hypothetical: during low-rate periods, some checking accounts and short-term Treasury bills paid essentially nothing, and the calculator correctly returns no growth rather than a misleading number.
FAQ
What is APY?
APY stands for Annual Percentage Yield. It is the effective annual rate of return after taking compounding into account, and it is the number US banks are required by Regulation DD to advertise on savings accounts, CDs, and money-market products. APY always assumes a full one-year holding period.
What is the difference between APY and APR?
APR (Annual Percentage Rate) is the nominal rate before compounding; APY is the real rate after compounding. On a deposit product the bank quotes APR and advertises APY; on a loan it quotes APR (which may also fold in fees). For a savings account, always compare APY — it is the only figure that tells you what you will actually earn.
How do I calculate APY by hand?
Use the formula APY = (1 + r/n)ⁿ − 1, where r is the nominal annual rate as a decimal and n is the number of compounding periods per year. For example, 5% compounded monthly: r = 0.05, n = 12, so APY = (1 + 0.05/12)¹² − 1 = 0.05116, or about 5.12%.
Is daily compounding really better than monthly?
Yes, but the gap is small. On a 5% nominal rate, monthly compounding gives 5.116% APY while daily compounding gives 5.127% — a difference of roughly $11 on a $10,000 balance over one year. The gap widens with larger balances and longer horizons, but for most depositors the rate itself matters far more than the compounding frequency.
Does APY include taxes or inflation?
No. APY is the gross nominal return before taxes and before inflation. Your after-tax real return is lower: interest from a savings account or CD is taxed as ordinary income at your federal (and often state) rate, and inflation erodes purchasing power. To estimate real growth, subtract your tax rate and the inflation rate from the APY.
What is a good APY on a high-yield savings account?
As of 2025–2026, competitive high-yield savings accounts pay APYs between 4.0% and 5.0%, while no-penalty and 12-month CDs range from 4.3% to 5.3%. Anything above 5.0% is worth a second look — confirm the institution is FDIC-insured and check whether the rate is a short-lived promotional teaser that will drop after a few months.
What happens if I withdraw early?
APY assumes the principal sits untouched for a full year. Withdrawing early — especially from a CD — usually triggers a penalty (often 90 to 365 days of interest) that reduces or wipes out the gain. The calculator models the no-withdrawal case; adjust the time horizon to reflect how long the money will actually stay in the account.
Disclaimer
This APY calculator is provided for informational purposes only and does not constitute financial, banking, or tax advice. APY estimates are based on the formula (1 + r/n)ⁿ − 1 and the inputs you enter; actual yields vary by institution, product, balance tier, promotional rate terms, and compounding convention. Banks may use 360-day or 365-day years, may cap compounding at month-end, and may change rates at any time. Always confirm the advertised APY and the account's fee schedule directly with a federally insured institution before depositing funds.