What Is APY? Annual Percentage Yield and How It Is Calculated

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Annual percentage yield (APY) is the total percentage return a deposit earns over one year once compounding is included. It combines two things into one figure: the account’s stated (nominal) interest rate and how often that interest is added to the balance. Because interest that has already been credited goes on to earn interest itself, APY is equal to or higher than the nominal rate. It is equal only when interest compounds once a year.

APY stands for annual percentage yield. In banking it is the standard figure for comparing savings accounts, money market accounts, certificates of deposit (CDs) and interest-bearing checking accounts. In the United States, banks must state it when they advertise those accounts.

What APY Measures

Every interest-bearing account has a nominal rate, the headline percentage before compounding. If a savings account pays a 5% nominal rate compounded monthly, the bank does not credit 5% once at year-end. It credits one-twelfth of 5% each month, and every credit raises the balance that next month’s interest is calculated on. After twelve months the account has grown by slightly more than 5%. That actual one-year growth rate is the APY.

The point of the measure is standardization. One account may compound daily, another monthly and a CD quarterly. Their nominal rates can’t be compared directly, because the same nominal rate produces different results under different compounding schedules. APY converts all of them into a single question: how much will this money grow in exactly one year?

The same concept appears outside banking as the effective annual rate (EAR) or effective annual yield. The math is identical. APY is the label used for deposit products.

The APY Formula

The standard formula is:

APY = (1 + r / n)^n − 1

where:

• r = the nominal annual interest rate, written as a decimal (5% = 0.05)
• n = the number of compounding periods per year (12 for monthly, 4 for quarterly, 365 for daily)

The term r / n is the interest rate applied each period. Raising (1 + r / n) to the power of n compounds it across the full year. Subtracting 1 leaves only the growth.

Step-by-step calculation

Take a 5% nominal rate compounded quarterly:

1. Divide the rate by the number of periods: 0.05 / 4 = 0.0125.
2. Add 1: 1.0125.
3. Raise to the number of periods: 1.0125^4 = 1.050945.
4. Subtract 1: 0.050945, or about 5.09% APY.

A $100 deposit at these terms would hold about $105.09 after one year. With simple interest, the result would be exactly $105.

How compounding frequency changes APY

The table holds the nominal rate fixed at 5% and changes only the compounding schedule.

Two patterns show up. First, more frequent compounding always raises the APY. Second, the gains shrink quickly. Moving from annual to monthly compounding adds about 0.12 percentage points, while moving from daily to continuous adds almost nothing.

Continuous compounding uses a different formula: APY = e^r − 1, where e is about 2.71828. For r = 0.05, e^0.05 − 1 = 5.127%. The larger the nominal rate, the bigger the gap between the nominal rate and the APY.

Working backward from APY

Advertisements usually quote the APY, not the nominal rate. To find the periodic rate behind an APY, reverse the formula:

Periodic rate = (1 + APY)^(1/n) − 1

For a 5% APY compounded monthly, (1.05)^(1/12) − 1 = 0.4074% per month. Multiplied by 12, that gives a nominal rate of about 4.889%. So a 5% APY with monthly compounding corresponds to a nominal rate a little under 5%.

The regulatory version

U.S. rules under the Truth in Savings Act (Regulation DD) also define APY in terms of what an account actually pays:

APY = 100 × [(1 + Interest / Principal)^(365 / Days in term) − 1]

Here “Interest” is the dollar interest earned on the principal over the term. This version produces the same result as the compounding formula for a standard one-year account. It also handles terms that aren’t a full year, such as a nine-month CD, by scaling the result to 365 days.

Is APY Monthly or Yearly?

APY is always a yearly figure. A savings account advertising a 3% APY does not pay 3% each month. It pays whatever monthly or daily rate produces 3% total growth over twelve months, assuming the rate doesn’t change and no money is withdrawn.

Dividing the APY by 12 gives only an approximation of each month’s interest, and the approximation runs slightly high. Consider a hypothetical $10,000 balance at a 3% APY compounded monthly:

• The true monthly rate is (1.03)^(1/12) − 1 = 0.2466%.
• First-month interest is about $24.66, not the $25.00 that 3% / 12 would suggest.
• Each later month earns a little more because the balance has grown.
• After twelve months the account holds about $10,300, which is the 3% APY.

The same logic applies to any rate. A 29% APY divided by 12 does not give the true monthly rate. It overstates it, because compounding already supplies part of the annual figure.

Interest can compound on one schedule and be credited on another. For example, an account might compound daily but post interest to the balance monthly. Regulation DD disclosures state both the compounding and crediting frequency, along with the balance method used (daily balance or average daily balance).

Example: Watching Compound Interest Build

APY exists because of compounding, so it helps to see compounding month by month. Take a hypothetical $1,000 deposit at a 6% nominal rate compounded monthly. The monthly rate is 0.06 / 12 = 0.5%.

• Month 1: $1,000 × 1.005 = $1,005.00. Interest is $5.00, earned only on the original deposit.
• Month 2: $1,005.00 × 1.005 = $1,010.03. Interest is $5.03, because the first month’s $5.00 is now earning interest too.
• Month 3: $1,010.03 × 1.005 = $1,015.08. Interest is $5.05.

Each month’s interest is slightly larger than the last, as long as the rate holds and nothing is withdrawn. After twelve months the balance is about $1,061.68, so the APY is 6.17%. Simple interest at 6% would have produced $1,060.

Over several years the gap widens. The multi-year version of the formula is:

Final amount = D × (1 + r / n)^(n × y)

where D is the initial deposit and y is the number of years. Using the earlier example of $100 at 5% compounded quarterly for four years: $100 × (1.0125)^16 = $121.99. With simple interest, the result would be $120. The difference is small on $100 but scales directly with the balance and with additional deposits.

How APY Is Used

Comparing accounts on equal terms

Suppose you are choosing between two hypothetical options:

• Option A: a one-year zero-coupon bond paying 6% at maturity.
• Option B: a money market account paying a 6% rate compounded monthly.

Both are quoted at 6%, but the money market account’s APY is (1.005)^12 − 1 = 6.17%. The bond pays once, so its effective yield stays at 6%. Comparing the headline rates would wrongly make the two look identical.

This is why U.S. banks must state the APY when they advertise interest-bearing deposit accounts. The Truth in Savings Act of 1991, implemented through Regulation DD, sets that requirement. Federally insured credit unions follow parallel rules from the National Credit Union Administration. Credit unions often call interest “dividends,” but the APY works the same way.

Matching yield to access and risk

APYs across deposit products tend to rise with how much access the customer gives up:

• Checking accounts keep money available for daily spending. Many pay little or no interest.
• Savings and money market accounts expect balances to stay put longer, which lets the bank lend the money out. They generally pay more than checking.
• CDs lock money up for a fixed term, usually with an early withdrawal penalty. In return they typically offer higher APYs, often more for longer terms.

At FDIC-insured banks and NCUA-insured credit unions, deposits are protected up to $250,000 per depositor, per institution, per ownership category. A higher APY at an insured institution doesn’t add credit risk within that limit.

The picture changes outside insured deposits. A brokerage cash sweep, a crypto lending product or a staking program may also quote an “APY.” The math still describes compounding, but the yield can depend on market conditions, platform risk or token prices, and it lacks deposit insurance.

A figure such as 100% APY means the balance would double in one year if the stated rate held for the full year. With any product, a very high APY says nothing about how likely that outcome is.

APY vs. Interest Rate vs. APR

These three terms are often confused because all are annual percentages.

• Interest rate (nominal rate): the base rate before compounding. It is the r in the formula.
• APY: the nominal rate with compounding included. It is used for money you earn.
• APR (annual percentage rate): the annual cost of borrowing. It is used for money you owe on loans, credit cards and mortgages.

The key difference is that APR, as disclosed under U.S. lending rules, is generally a simple annualized rate. It does not reflect intra-year compounding. It can, however, fold in certain loan fees, which APY does not do on the deposit side. A full treatment of how lenders build that number is in the guide to APR.

APR can be converted to an effective rate with the same formula as APY. A 7% APR with monthly compounding produces an effective annual rate of (1 + 0.07/12)^12 − 1 = 7.23%. On a credit card with that APR and a balance carried all year, the effective cost is closer to 7.23% than to 7%. The difference grows with the size of the APR.

The direction of the incentive also differs. When saving, a higher APY is better, and compounding works for you. When borrowing, compounding works against you, so the effective cost is higher than the APR suggests.

APY vs. APYE

On periodic account statements, banks may show the annual percentage yield earned (APYE). APY is a forward-looking disclosure based on the rate and an assumed full year. APYE reflects what the account actually earned during the statement period, based on the interest credited and the balance held. If the balance moved around or a variable rate changed mid-period, the two figures can differ.

Fixed vs. Variable APY

A fixed APY stays the same for a set term. CDs are the standard example: the rate is locked from opening until maturity.

A variable APY can be changed by the institution, and it typically moves with broader interest rates, including changes in Federal Reserve policy. Most savings, money market and interest checking accounts carry variable rates. The advertised APY on a variable-rate account reflects today’s rate only. It is not a promise for the full year.

Neither type is better in every situation. A fixed APY protects against falling rates but misses out if rates rise. A variable APY captures rising rates but drops when rates fall.

Tiered and promotional APYs

Some accounts pay different APYs on different portions of the balance, or a higher introductory rate for a limited period. Consider a hypothetical account paying 5% APY on the first $500 and 1% APY on everything above that. On a $5,000 balance held for one year:

• $500 × 5% = $25
• $4,500 × 1% = $45
• Total: $70, a blended yield of 1.4%

The headline 5% applies to only a tenth of the money. For tiered accounts, the blended figure is what determines actual earnings.

Limitations of APY

APY answers one question well: how fast a deposit grows over a year at a given rate and compounding schedule. Several things fall outside it.

Fees. The APY calculation doesn’t subtract monthly maintenance fees, minimum-balance fees or other account charges. A hypothetical $5 monthly fee on a $1,000 balance removes $60 a year. That more than cancels a 5% APY on that balance.

Rate changes. On a variable-rate account, the APY assumes today’s rate lasts twelve months. It rarely describes the full year exactly.

Taxes. In the U.S., interest is generally taxed as ordinary income in the year it is credited. After-tax yield is lower than the APY.

Inflation. APY is a nominal return. The real return is roughly the APY minus inflation. Comparing a yield against the U.S. inflation rate by year shows whether savings gained or lost purchasing power.

Bonuses and penalties. Sign-up bonuses aren’t included in APY, and neither are CD early withdrawal penalties.

To put a bonus on a comparable footing, divide the bonus by the deposit and scale it to a year. For a hypothetical $300 bonus on $15,000 held for 90 days, the return is 2% over the period. That annualizes to about 8.1% simple (2% × 365 / 90). Compounded, it is about 8.4% ((1.02)^(365/90) − 1). The result is only meaningful if you would hold the money for exactly that period under those terms.

What Makes a Good APY?

A good APY is relative, not a fixed number. Deposit yields generally rise when the Federal Reserve raises rates and fall when it cuts, so a rate that looks strong in one year can look weak in another. Useful benchmarks:

• What comparable insured accounts pay at the same time
• What a CD of matching length pays
• Whether the APY keeps up with inflation

Online banks and credit unions often price their savings accounts above the rates paid on many traditional branch savings accounts. Even so, the comparison should be made between account types with similar access, fees and minimum balance requirements.

FAQs

The Bottom Line

APY matters most to savers choosing among savings accounts, money market accounts, CDs and interest checking, because it puts different compounding schedules on equal terms. Use it to compare similar insured accounts, then check what it leaves out: fees, taxes, inflation, bonuses, penalties and future rate changes on variable accounts. For tiered accounts, the blended yield on your actual balance shows what you will really earn.