APY Calculator
This APY calculator converts a nominal interest rate and its compounding frequency into the effective annual percentage yield — the number that tells you what an account really pays over a year, shown both as a rate and in dollars on your balance.
Free tool · No sign-up · Using it has no impact on your credit score
The stated annual rate before compounding — sometimes listed as the "interest rate" next to the APY.
Used to show the yield in dollars.
APY
4.3%
A 4.20% nominal rate at this compounding frequency actually yields 4.29% over a full year.
Compounding boost
0.1%
Compounding adds 0.09 percentage points on top of the stated rate over a year.
One year of interest
$429
On a $10,000 balance, this yield pays $429 in a year.
Nominal rate vs APY
What this calculator tells you
Banks quote two numbers that sound alike but aren't: the nominal interest rate, and the APY. The nominal rate is the raw annual figure before compounding; the APY is what you actually earn over a year once each period's interest starts earning its own. This calculator converts one into the other for any compounding frequency, then prices the yield in dollars on your balance so the percentage stops being abstract.
The conversion matters most when comparing accounts. Two banks advertising "4.2%" can pay different amounts if one compounds daily and the other annually — and an account advertising a slightly lower nominal rate with daily compounding can out-earn a higher nominal rate compounded annually. APY is the standardized, apples-to-apples number; U.S. banks are required by federal Truth in Savings rules to disclose it precisely so you can compare without doing this math.
How it works
The calculator splits the nominal rate across the year's compounding periods — 365 slices for daily, 12 for monthly — applies each slice to a growing balance, and measures the total growth after one full year. That measured growth, expressed as a percentage, is the APY. The dollar figure applies the same one-year growth to the balance you enter.
More frequent compounding always nudges APY above the nominal rate, but with quickly diminishing returns: most of the boost arrives going from annual to monthly, and daily adds only a hair more.
Formula and assumptions
APY = (1 + r/n)^n − 1, where r is the nominal annual rate as a decimal and n is the compounding periods per year. In the default example, 4.2% compounded daily gives (1 + 0.042/365)^365 − 1 ≈ 4.29% — the extra 0.09 points is compounding's contribution. One year of interest on a balance B is simply B × APY.
Assumptions: the rate holds for a full year (savings rates are variable in practice and can change any day), the balance stays untouched with no deposits or withdrawals, and the result is pre-tax. Promotional rates that expire mid-year will earn less than the APY implies — the APY is honest only for as long as the rate survives.
Example scenario
A 4.2% nominal rate compounded daily on a $10,000 balance plays out like this:
- APY
- 4.3%
- Compounding boost
- 0.1%
- One year of interest
- $429
Is my result good or bad?
Context for the number: competitive high-yield savings accounts have recently paid roughly 4–4.5% APY, top nationally available CDs sit in the same band, and the default rate at the largest branch banks is about 0.05% APY. On a $10,000 balance, that's roughly $430 a year versus $5 — an eighty-to-ninety-fold gap for money doing exactly the same job. If your APY starts with a zero, the account is the problem, not the balance.
Don't over-read small APY differences near the top of the market, though. The gap between 4.30% and 4.45% is worth $15 a year on $10,000 — routinely erased by a single monthly fee, a minimum-balance requirement you occasionally miss, or a promo rate that steps down after 90 days. Compare APY first to eliminate the terrible options, then let fees, minimums, and rate history pick among the good ones.
Frequently asked questions
What's the difference between APY and interest rate (APR)?
The interest rate (or APR) is the nominal annual figure before compounding; APY is the effective amount you earn over a year after compounding is included. APY is always equal to or higher than the nominal rate — equal only when interest compounds exactly once a year. When comparing savings products, APY is the number to use; APR matters more on the borrowing side, where it works against you.
Why do banks advertise APY instead of the nominal rate?
Partly because it's the bigger number, but mostly because federal Truth in Savings rules require deposit accounts to disclose APY using a standardized formula. That regulation works in your favor: every bank computes APY the same way, so a 4.30% APY at one bank pays the same dollars as 4.30% at another, regardless of how each one compounds internally.
How does compounding frequency change APY?
Each step up in frequency raises APY, but the gains shrink fast. At a 4.2% nominal rate: annual compounding yields exactly 4.20%, monthly about 4.28%, and daily about 4.29% — so annual-to-monthly is worth about $8 a year per $10,000, while monthly-to-daily is worth pennies. Frequency is worth checking, but it should never outrank the rate itself in your comparison.
Is a higher APY always the better account?
Not automatically. A monthly maintenance fee of $5 erases $60 a year — more than the gap between most competing high-yield accounts. Also check minimum-balance requirements to earn the advertised rate, whether the APY is a promotional teaser that steps down after a few months, and withdrawal or transfer limits. The best account is the highest APY you'll reliably receive with no fees on your actual balance and habits.
Do savings APYs change over time?
Yes — savings and money market APYs are variable and move with the Federal Reserve's rate decisions, usually within weeks of a change. That's why the same account paid near 0.5% in 2021 and over 4% more recently. If you want to lock today's yield, a CD fixes the rate for its term; the trade-off is losing access to the money without an early-withdrawal penalty.
How is savings interest taxed?
Interest from savings accounts, money market accounts, and CDs is taxed as ordinary income at your marginal federal rate (plus state tax where applicable) in the year it's credited. Your bank sends a 1099-INT once you earn $10 or more. Practically, a 4.3% APY nets roughly 3.4% for someone in the 22% bracket — still dramatically better than 0.05%, but worth remembering when comparing against tax-advantaged options.
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Estimates only. Results assume the inputs you provide and standard fixed-rate math. Actual lender offers, rates, and terms are determined by lending partners based on your credit profile and state. BankMinistry is not a lender. Not financial advice.