Banking

How APY Works

Reviewed by Unpack Money Research Desk · Updated October 2026 · Our review process

Quick answer

APY — annual percentage yield — is the effective yearly return on a deposit, including the effect of compounding. A 4.00% APY means $10,000 grows to $10,400 in one year, regardless of whether interest compounds daily, monthly, or annually. It's the apples-to-apples number for comparing savings accounts: the same APY always means the same annual growth.

APY in one sentence

APY answers a simple question: if I leave my money alone for a year, by what percentage does it grow? That percentage bakes in compounding — interest earning interest — so it reflects what actually lands in your account. Banks are required to quote APY in a standardized way, which is what makes it the reliable comparison number across institutions.

The practical upshot: when two savings accounts show the same APY, they produce the same growth over a year even if one compounds daily and the other monthly. The compounding frequency is already inside the APY figure.

Where compounding comes in

Banks often quote a nominal interest rate and then compound it on a schedule — daily, monthly, quarterly. The APY converts that schedule into an annual figure with the formula A = P(1 + r/n)^(nt), where P is the principal, r the nominal rate, n the compounding periods per year, and t the years.

Walk through it: a hypothetical nominal rate of 3.92%, compounded monthly, on $10,000. Each month's rate is 0.0392 ÷ 12. After 12 months: $10,000 × (1 + 0.0392/12)^12 ≈ $10,399.12. The account grew 3.99% — so the APY is 3.99%, a touch above the 3.92% nominal rate. That small lift is compounding doing its quiet work, and the APY is simply its annual summary.

APY vs. interest rate vs. APR

Three terms, three jobs. The nominal interest rate is the base rate before compounding is factored in. APY is that rate translated into effective annual yield — always equal to or higher than the nominal rate when compounding is more frequent than annually. APR (annual percentage rate) belongs to the borrowing side: it's what you pay on loans and credit cards, and it typically excludes compounding effects.

The shopping rule: compare savings accounts by APY to APY. If a bank advertises only a nominal 'interest rate,' ask for (or compute) the APY before comparing it to anything else.

Why APY moves

Savings APYs are variable — banks adjust them as the broader rate environment shifts. When benchmark rates rise, competitive banks typically lift their savings APYs to attract deposits; when benchmarks fall, APYs drift down. Online banks tend to move faster in both directions than traditional banks.

This variability is the main trade-off of a high-yield account versus a CD: the HYSA's APY is today's number, not a contract. It also means there's no bad time to open one — you earn whatever the current APY is from day one, and you can move the money if a better APY appears elsewhere.

Using APY when you shop

Rank candidates by APY first — it's the single number that captures yield. Then check what the APY doesn't show: monthly fees (which subtract from your effective return), minimum-balance requirements to earn the quoted APY, and withdrawal or transfer limits. An account with a slightly lower APY and zero fees usually beats a higher APY with a fee you can't avoid.

Finally, confirm the APY applies to your entire balance. Some accounts advertise a high APY that only applies up to a balance cap, with a much lower rate above it. The fine print decides what you actually earn.

At a glance

Nominal rate vs. APY with monthly compounding (illustrative)

What this means for you

APY is the only yield number you need for comparing savings accounts: same APY, same annual growth, regardless of compounding schedule. Learn the formula once so the concept sticks, then shop on APY — and read the fee schedule before you commit.

Keep unpacking