A savings account advertises 4.5%, but the interest you actually earn depends on how often the bank adds it to your balance. An APY calculator converts the nominal rate and compounding frequency into the effective annual yield, so two accounts with the same headline rate can be compared on the number that matters.
APY is the effective annual return on a deposit after compounding. It assumes interest stays in the account and is reinvested, and it does not reflect taxes or fees that reduce your actual return.
Figures in this article were reproduced from the calculator itself.
How to Use the APY Calculator
- Enter the advertised rate: Type the Nominal Annual Rate (% APR), which is the rate before compounding is factored in.
- Pick the compounding: Choose a Compounding Frequency, such as Daily, Monthly, Quarterly, Annually, or Continuous, to match how the account credits interest.
- Optionally add a balance: Enter a Deposit Amount and, when a deposit is entered, a Growth Term (Months) to see illustrative balance growth; leave both blank to calculate APY only.
- Calculate: Click Calculate to see the Annual Percentage Yield (APY), the Rate Per Period, and, when a deposit is given, the Balance After Term and Interest Earned.
The result assumes the rate and compounding stay constant for the term and does not model withdrawals, rate changes, or fees an account might charge.
What APY Really Tells You About Your Savings
Compounding in Action: Why APY Is Always Higher Than Nominal Rate
Compounding means interest earns interest. At a 4.5% nominal rate compounded monthly, each month earns 0.375% of the balance. The next month's interest is calculated on the original deposit plus the first month's interest, so the effective annual rate rises to 4.5940%.
The gap grows with the nominal rate and the number of compounding periods. It is zero when interest compounds once a year, because nothing is reinvested during the year. APY is higher whenever compounding happens more than once annually and the rate is positive.
Why Deposit Accounts Disclose APY
The standardized figure is not a marketing choice. Regulation DD (12 CFR Part 1030) defines annual percentage yield as a rate reflecting the total interest paid on an account over a 365-day period, based on the interest rate and the frequency of compounding, and requires the disclosed APY to be rounded to the nearest 0.01 percentage point, as the regulation text sets out. That single definition is what makes two banks' APYs comparable even when their fee schedules and balance tiers are not.
An APY is also a snapshot rather than a promise. Deposit accounts can be variable-rate, and a quoted APY is calculated for a specific date and often a specific balance tier. Promotional APYs commonly apply to a limited balance or a limited period, after which the account reverts to its standard rate. Read the rate sheet to see what applies after the promotional window, and compare the APY alongside fees, minimum-balance conditions, and withdrawal terms. It covers deposit accounts, not investment products such as stocks or mutual funds.
Illustrative promotional example, computed with the same growth formula the tool applies to each window: $10,000 at a 4.75% promotional APY for 3 months, then a 1.5% standard APY for the remaining 9 months, reaches about $10,230.29 after a year. Held at 1.5% APY the whole year, the same deposit reaches $10,150.00, so the three-month promo adds $80.29 — much less than the $325 gap between 4.75% and 1.5% headline rates suggests, because the high rate applies to a quarter of the year. A 4.75% APY sustained for all 12 months would reach $10,475.00. The promo is still worth taking; it just should not be annualized in your head.
The Mathematical APY Formula Explained
The Standard Equation: APY = (1 + r/n)^n − 1
In the formula, r is the nominal annual rate written as a decimal and n is the number of compounding periods per year. For daily compounding, n is 365. For monthly, n is 12. The result is a decimal, so multiply by 100 to express it as a percentage.
Continuous compounding uses a different expression: APY = e^r − 1, where e is approximately 2.71828. The calculator includes this option because some models use continuous compounding even though most consumer deposit accounts do not.
Step-by-Step Conversion for Daily vs Monthly Compounding
For 4.5% compounded monthly, divide 0.045 by 12, add 1, raise to the 12th power, and subtract 1. The APY is 4.5940%.
For daily compounding, divide by 365, add 1, raise to the 365th power, and subtract 1. The APY is 4.6025%. The daily rate is smaller but applied more often.
With a deposit and term, the tool uses APY as the effective annual rate. $10,000 at 4.6025% for 12 months reaches $10,460.25. At 5% nominal compounded daily, APY is 5.1267% and the balance reaches $10,512.67.
Compounding Frequency Comparison Table
Evaluating Annual, Semi-Annual, Quarterly, Monthly, and Daily Yields
The table holds the nominal rate at 4.5% and changes only the compounding frequency.
| Frequency | Periods per year | APY |
|---|---|---|
| Annual | 1 | 4.5000% |
| Semi-annual | 2 | 4.5506% |
| Quarterly | 4 | 4.5765% |
| Monthly | 12 | 4.5940% |
| Weekly | 52 | 4.6008% |
| Daily | 365 | 4.6025% |
| Continuous | Infinite | 4.6028% |
The tool offers annual, quarterly, monthly, weekly, daily, and continuous. Semi-annual is shown for comparison. Each step up in frequency adds less.
How Much Daily Compounding Actually Adds
Moving from annual to daily compounding adds about 0.1025 percentage points at a 4.5% nominal rate, or roughly $10.25 per $10,000 per year. Moving from monthly to daily adds only about 0.0085 percentage points, or less than $1 per $10,000 per year.
Daily compounding is rarely a reason to choose an account. Nominal rate, fees, and minimums usually matter more.
Two Accounts, Same Headline APY: What a Monthly Fee Does
Illustrative case: two $10,000 deposits each advertise a 4.5% APY for a year. One charges a $5 monthly maintenance fee, deducted from the balance; one charges nothing. The fee-free account ends the year at $10,460.25. The fee-charging account ends at $10,388.77, because each deduction also removes the interest that money would have earned — $60 of fees costs $71.48 all in. The same comparison against a fee-free account at 4.25% APY ($10,425.00) still favors the fee-free account by $36.23: at consumer deposit rates, a fraction of a point in yield rarely outruns a monthly fee. Fee figures are illustrations, not current account terms.
APY Assumes You Leave the Interest Alone
Every APY figure assumes the interest compounds for a full year. Withdraw it each month and the balance never grows, so the account pays the nominal rate instead. On $10,000 at 4.5% compounded monthly, leaving the interest in produces $459.40 over a year, while taking the monthly interest out produces $450.00. The $9.40 difference is the entire value of compounding at that rate, and it disappears the moment the interest is spent.
Key Distinction: APY vs APR
APY: What You Earn on Deposits
APY measures what a deposit earns, including compounding. A 5% nominal rate compounded monthly produces a 5.1162% APY, a better description of the year's growth than the 5% headline.
It is the right comparison for savings accounts and certificates of deposit. The CD calculator applies the same idea to a fixed term.
APR: The Borrowing Expense (What Lenders Charge on Debt)
APR is a borrowing-cost measure, not a deposit yield. For many closed-end loans, it includes the interest rate and certain finance charges; disclosures vary by product. The CFPB explains the difference between a loan's interest rate and APR in its loan APR guide.
APY and APR are not interchangeable. One is a return to you, the other a cost, and their disclosure rules differ. Use the APR calculator for borrowing costs and this tool for deposit yields. The compound interest calculator handles recurring contributions, which this APY tool does not.
Regulation DD / Truth in Savings Act context: the APY definition and 0.01-percentage-point rounding rule described on this page were verified against 12 CFR Part 1030 as of October 2026. The regulation itself is static; check for amendments at eCFR Part 1030 if using this page after 2026.
Last verified: October 2026. Calculator figures are outputs for the inputs entered; they are not live quotes, current rates, or an offer.