Reading Deposit APY: Compounding, Variable Rates, and Fair Comparisons

When you compare savings products, the useful shopping label is usually APY—annual percentage yield—not the raw nominal rate alone. Sorted Finance treats APY as a standardized disclosure: it answers “if this rate and compounding schedule held for a year and you left the money alone, what yearly yield would you earn?” It does not answer “will next March’s rate match today’s flyer?”

Banks and credit unions generally quote APY on consumer deposits so products that compound on different clocks can be compared. Two accounts can share a nominal rate and still show different APYs if one compounds daily and the other monthly. APY folds that difference into one percentage. Compare APY to APY.

Nominal rate versus yield

The interest rate (sometimes called the nominal rate) is what gets applied each compounding period. APY is that rate after compounding is recognized. When interest is credited more than once a year, APY sits slightly above the nominal rate. Credited only once a year, the two match.

“3.85% interest, compounded daily” is not the same sentence as “3.85% APY.” The first needs the compounding schedule; the second already includes it.

Most savings and money market APYs are variable. Many CD APYs are fixed for the term if you hold to maturity, subject to the account agreement and early-withdrawal rules.

Why regulators push a common yardstick

Truth in Savings rules exist so deposit shoppers can compare products without reverse-engineering every bank’s compounding clock. APY is that yardstick. It still says nothing about monthly fees, minimum balances, or how easily you can move money out.

Turning a rate into APY

Compounding means credited interest joins the balance, so later periods calculate against a larger amount.

Here r is the nominal annual rate as a decimal and n is compounding periods per year (often 365 for daily, 12 for monthly). Multiply by 100 for a percentage. The formula assumes a constant rate, no deposits or withdrawals, and interest left in place—conditions real accounts often break.

How much does compounding frequency matter?

Holding the nominal rate fixed, daily beats monthly by a little, and monthly beats annual by a little. The gap is usually smaller than the spread between two banks’ advertised APYs—or smaller than a maintenance fee on a modest balance.

What usually matters more:

• The APY itself (compounding already included)
• Whether the APY is a teaser and when it ends
• Fees that erase interest on small balances
• Whether you can leave the cash parked for the period you care about

What APY includes—and what it leaves out

APY measures interest. It does not subtract income tax. Interest credited to ordinary savings is generally taxable in the year it is credited, even if you never withdraw it. A Form 1099-INT, if issued, reports that interest.

APY also ignores sign-up cash, ATM rebates, inflation’s bite on purchasing power, and the opportunity cost of cash versus paying high-rate debt.

Treat APY as an annualized interest label under stated assumptions—not a guaranteed return, not an after-tax figure, and not a ranking of which institution fits every household.

Shopping savings, money markets, and CDs

All three quote APY; they are still different jobs. Liquid savings and many money market deposit accounts usually carry variable APYs. CDs typically lock a rate for a term and charge a penalty for early withdrawal. Money market deposit accounts may add check or debit access with their own minimums—and they are not money market mutual funds.

A practical checklist:

1. Match product type first, then compare APYs
2. Note variable versus term-fixed
3. Read balance tiers and caps
4. Check fees, minimums, and transfer rules
5. Confirm federal deposit insurance for your ownership category and institution

Insurance protects principal within limits if the institution fails. It does not lock the APY.

Worked sketch: $14,500 at a stated rate

Illustration only—not an offer.

Suppose a savings account quotes a 3.95% nominal annual rate, compounded daily (n = 365). You deposit $14,500 on day one, add nothing, withdraw nothing, and the rate never moves for 365 days.

APY = (1 + 0.0395 / 365)^365 − 1 ≈ 4.03%. On $14,500, a full year of interest at that APY would be about $584 if every assumption held. The same 3.95% credited once at year-end would produce about $573. The gap is the compounding edge in this example—real, but modest.

Now break an assumption: the bank cuts the variable rate after five months. Last month’s APY no longer describes the remaining seven months. Actual interest becomes a blend.

Add a $6 monthly maintenance fee ($72 a year). On $14,500 here, that fee can outweigh the daily-versus-annual compounding edge.

Use the Sorted Finance Compound Interest Calculator to test other balances and rates. Every ending balance is only as realistic as the inputs you chose.

Teasers, tiers, and fine print

Online savings APYs often move with the broader rate environment. Some banks run promotional APYs for new customers or for balances under a cap, then step down. Read duration, qualifying balance, and the post-promo rate.

Rules that can shrink what you keep: minimum daily balances, APY paid only up to a dollar limit, linked-checking requirements, or limited free withdrawals. None of those features is automatically a bad deal—they are reasons not to stop at the bold percentage.

When APY is the wrong tool

APY is right for comparing interest on similar deposits. It is wrong for ranking stock or fund returns. It cannot tell you whether to keep an emergency reserve in cash, pay a card, or fund a retirement account. It also cannot outrun inflation: if prices rise faster than your yield, purchasing power can fall while the balance ticks up.

Past APY is not a forecast. Label every calculator rate as an assumption and every ending balance as a scenario.

Sorted takeaway

Shop deposits on APY, then read fees, tiers, and whether the rate can move. Use the compounding formula to understand the disclosure—not to predict next year’s interest. A CD can lock a rate for a term if you hold it; most savings APYs cannot. At Sorted Finance, treat the headline percentage as a comparison label, then run your own balance through the Compound Interest Calculator before you move cash.