APY Calculator

APY and nominal interest rate are not the same

A nominal annual rate states the annualized rate before the effect of within-year compounding is incorporated. APY expresses the effective one-year growth produced when interest is compounded and left in the account.

At a positive rate, monthly or daily compounding normally makes APY slightly higher than the nominal rate. When compounding is annual, the nominal annual rate and APY are the same in this simplified model.

How APY is calculated

APY = (1 + nominal annual rate ÷ compounding periods)^(compounding periods) − 1. The periodic rate is the nominal annual rate divided by the number of compounding periods.

The example deposit is then multiplied by 1 + APY to show the one-year ending balance before fees, taxes, withdrawals or rate changes.

Worked example: monthly compounding

A 5% nominal annual rate compounded monthly has a slightly higher APY than 5% because interest is credited during the year and begins earning interest itself. On a 10,000 example deposit, the one-year interest is therefore slightly above 500 under the constant-rate assumption.

Change monthly compounding to annual compounding while leaving the nominal rate unchanged to isolate the effect of frequency.

Use APY for like-for-like deposit comparisons

APY can make products with different compounding schedules easier to compare, but it is not the only feature that matters. Minimum balances, promotional periods, account fees, withdrawal limits and whether the rate can change can affect the value you actually receive.

For a certificate of deposit, also check the term and early-withdrawal penalty. For a savings account, check whether the APY is variable or conditional on account activity.

Avoid double-compounding a quoted APY

If a product already quotes APY, do not enter that APY as a nominal rate and then choose monthly compounding when trying to replicate the advertised one-year yield. That would apply compounding twice conceptually.

Use the APY as the effective annual yield for a direct one-year growth calculation, or use the underlying nominal rate and stated frequency when both are known.

APY is an annual comparison measure, not a promise for every holding period

APY is designed to express the effect of compounding over a full year under the stated rate and compounding convention. If money remains in an account for only part of a year, the interest earned depends on the actual number of periods, the account’s crediting method and whether the rate stays unchanged. Simply multiplying APY by the fraction of a year is only an approximation.

This matters when comparing a short certificate, promotional savings rate or account you may close before a year has passed. Use the product’s actual term and disclosure for the cash amount you expect to receive, while using APY mainly as a standardized annual comparison measure.

For comparisons, keep the deposit amount the same and change only the rate or compounding convention. That makes the yield difference visible without mixing it with a larger balance. When two accounts both publish APY, compare those published APYs directly and then review fees, conditions and access rules instead of reverse-engineering a nominal rate unnecessarily.

Use The Result In The Next Calculation

Use APY to compare deposit products on a common annual-yield basis. If you already know the APY and term of a certificate of deposit, move to the CD calculator instead of converting the rate again.