APY vs. APR on CDs: What's the Real Difference?

よくある質問

• Which is bigger on a CD, APY or APR?

  APY is bigger whenever interest compounds more than once a year, because it captures the effect of interest earning interest within the year, while APR is only the nominal rate annualized by simple multiplication. The two figures are equal only under annual compounding, where there is a single period a year and nothing left to compound before the year ends; introduce any more frequent schedule and APY pulls ahead of APR by a small but real margin. A CD disclosing a 4.40% nominal rate compounded daily converts to an APY of about 4.50% — apply that APY to a $10,000 deposit for 12 months and it matures at $10,450.00, a $450.00 gain, while the bank's own APR figure of 4.40% describes the same account from the other side of the same formula. The gap widens further as either the rate itself or the compounding frequency increases, though it rarely grows large enough on typical CD rates to flip which of two offers is the better one.

• Why do banks advertise APY instead of APR?

  Banks advertise APY instead of a nominal rate because Regulation DD requires it specifically so savers can compare offers from banks that compound on different schedules — daily, monthly, or quarterly — using one consistent, already-annualized number. An APY has the effect of compounding built into it, so multiplying your principal by it directly tells you what you will actually earn over a year, without requiring you to separately account for how often the bank credits interest internally. On a $10,000 CD advertised at 4.50% APY, the maturity value after 12 months is simply $10,450.00, computed as 10,000 × 1.045, regardless of whether the bank compounds that rate daily, monthly, or quarterly behind the scenes. A nominal rate quoted without an APY qualifier does not carry this convenience — you would need to convert it yourself using the compounding formula before it becomes directly comparable to another bank's disclosed APY figure.

• Does compounding frequency change the APY?

  Yes, but only up to a point — a given nominal rate produces a higher APY the more frequently it compounds, though most of that lift happens by the time you reach monthly compounding. Each additional compounding period lets a smaller sliver of interest start earning interest of its own sooner, and the effect diminishes as the periods get shorter, since there is only so much a year can hold. On a 4.50% nominal annual rate, annual compounding leaves the APY at exactly 4.50%, monthly compounding lifts it to about 4.5940%, and daily compounding lifts it further still to about 4.6025% — a climb of roughly 0.10 percentage points from annual to daily, most of which is already captured by monthly. That is why comparing two CDs' disclosed APY figures directly is normally sufficient; chasing daily compounding specifically, once you already have the APY, adds very little beyond what a monthly-compounding CD at the same rate would deliver.

• Can two CDs have the same APY but different APR?

  Yes — two CDs compounding at different frequencies need different nominal APRs to land on the identical effective APY, because less frequent compounding needs a larger nominal push to reach the same final result. A CD compounding monthly, for instance, requires a slightly higher stated APR than one compounding daily to produce the same APY, simply because it has fewer opportunities during the year for interest to earn interest on itself. A CD disclosing a 4.4020% APR compounded daily and a separate CD disclosing a 4.4098% APR compounded monthly both convert to approximately 4.50% APY, and on a $10,000 deposit for 12 months, both mature at the identical $10,450.00 despite the different APR figures on their disclosures. This is exactly why comparing APR to APR across banks with different compounding schedules is unreliable, and why converting everything to APY first is the only way to compare two CDs correctly.

• Is APY guaranteed for the whole term of a CD?

  On a standard fixed-rate CD, yes — the APY disclosed at opening holds for the entire term regardless of what happens to market rates afterward, since the bank has committed to a fixed nominal rate underneath that APY figure for the life of the account. This guarantee is what separates a CD from a savings account, where the disclosed APY can change at the bank's discretion at any time; a CD's APY, once quoted at funding, is contractually fixed until maturity. On a $10,000 CD opened at 4.50% APY, compounded daily, for a 12-month term, the account matures at $10,450.00 whether market rates rise, fall, or hold steady during that year — the APY you locked in at opening is the APY you actually receive. Variable, bump-up, and step-up CDs are the named exceptions, where the rate, and therefore the APY, can change on terms specifically disclosed at account opening rather than being fixed for the full term.

• Does a CD's APY change if I choose monthly instead of daily compounding?

  Yes, slightly, if the underlying nominal rate stays the same — monthly compounding produces a marginally lower APY than daily compounding, because interest has fewer opportunities during the year to be credited and start earning interest of its own. On a 4.50% nominal annual rate, monthly compounding produces an APY of about 4.5940%, while daily compounding on that identical nominal rate produces about 4.6025% — a difference small enough that it rarely changes which of two CDs is the better choice. On a $10,000 deposit for 12 months, that gap works out to about $10,459.40 versus $10,460.25 at maturity, well under a dollar of difference, not enough to justify choosing a lower nominal rate purely to get daily crediting instead of monthly. In practice, banks usually quote the APY directly rather than asking you to select a compounding frequency yourself, so this comparison is normally already resolved for you before you ever see the rate sheet.