- Effective annual yield reflects compounding.
- Disclosure labels and the costs included in APR differ across markets.
- Fees and product rules still matter.
An effective annual yield incorporates compounding. It may be labeled APY, AER, or another term depending on the market. APR is used in borrowing disclosures, but its prescribed calculation and included costs depend on the jurisdiction and product. Labels alone do not establish comparability.
This guide uses APY for effective annual yield and a nominal annual interest rate for the calculator arithmetic. Local disclosure rules and the actual contract remain necessary when comparing offers.
What compounding changes
A nominal 5% annual rate compounded monthly produces an effective annual yield of about 5.12%, assuming the rate is constant and interest stays in the account. The formula is (1 + nominal rate / 12)^12 − 1.
The US Regulation DD calculation guidance is one example of a formal disclosure framework. It does not establish disclosure law for other countries.
The example uses a hypothetical rate, not a current account offer. The difference comes from earning interest on interest within the year.
Why borrowing needs another layer
The APR shown for a card does not tell you the exact next interest charge by itself. Balance calculation, statement dates, transaction types, grace periods, and payment allocation can all matter.
A promotional offer may also apply to only one kind of balance for a limited period. The headline rate needs to be read alongside the issuer’s terms.
Compare the complete account
For savings, check whether the APY is variable, whether a balance tier or qualification applies, and whether fees offset part of the interest. For credit, check the applicable interest rate, the costs included in any disclosed APR, separately charged fees, and what causes rates to change. Do not enter a fee-inclusive disclosure rate as a nominal interest rate without checking the model.
Match the calculator input
Our savings calculator expects a nominal annual rate with monthly compounding. Converting an effective annual yield to its monthly-equivalent nominal rate requires 12 × ((1 + APY)^(1/12) − 1). All rates in the formula are decimals.
Using the right label makes a numerical comparison meaningful; it does not replace the actual account disclosures.