APY in plain English
APY tells you what a balance would earn over one year if interest compounds and remains in the account under the stated assumptions. When interest is added during the year, later interest can earn interest too.
That compounding effect means APY is usually higher than the nominal annual rate when compounding happens more than once per year.
When to use the APY Calculator
Use the APY Calculator when you know a nominal annual rate and compounding frequency and want the effective annual yield. It can help compare daily, monthly, quarterly, and annual compounding.
APY is useful for savings accounts and interest comparisons, but it does not capture fees, balance caps, variable rates, taxes, or investment risk.
APY versus investment return
APY is often used for stated interest products. Investment returns are different because values can rise or fall and returns are uncertain.
When planning investments, compare APY concepts with compound interest, CAGR, inflation-adjusted return, and real return so the assumptions are clear.