How to use the APY calculator
Use the calculator to convert a nominal annual rate and compounding frequency into APY. Add a deposit and time held if you also want an ending-balance projection. A blank deposit is treated as zero, so no projection is shown.
Enter the rate and compounding frequency
- Enter a rate from 0 to 100 in Nominal (stated) annual rate (%).
- Choose Compounding frequency: Annually, Semi-annually, Quarterly, Monthly, Bi-weekly, Weekly, Daily, or Continuous.
- Keep the rate fixed for the calculation; the tool does not apply live or changing rates.
Add an optional balance projection
- Enter 0 or more in Deposit amount ($, optional). A blank value is treated as zero; an explicit zero is accepted but produces no projection.
- Enter Time held (years, optional), or leave it blank to use 1 year. An entered value must be greater than 0 and no more than 100 years.
When the deposit is greater than zero, the projection uses Principal x (1 + APY)^Years, including non-whole-year values. It estimates an ending balance and interest earned; it does not simulate individual deposits, withdrawals, or transaction timing.
Calculate, review, and reuse the result
- Click Calculate to display APY, the nominal rate, the selected frequency, and selected assumptions. The periodic rate is shown for non-continuous frequencies.
- Review the displayed formula and values. APY uses four decimal places, nominal rate three, periodic rate six, and monetary values two.
- Use the available result actions:
- Click Copy result to copy the output. If copying fails, the interface displays Could not copy - select and copy manually.
- Click Download result (.txt) to create
apy-calculator-result.txt. - Click Reset to clear the calculator state.
Validation and calculation limits
Invalid entries show an error and hide the result. The nominal rate must be between 0 and 100, the optional deposit must be 0 or greater, and entered time held must be greater than 0 and no more than 100 years.
The calculator assumes a fixed rate and frequency. It does not model fees, taxes, withdrawals, tiered rates, promotional periods, or rate changes, and it is not personalized financial advice. The formula and selected assumptions are shown, but not every internal calculation value.
Privacy and page data behavior
Calculator inputs are processed by the page's calculation script without a calculator form submission. The page also has a subscription form: it POSTs the entered email to /assets/subscribe.php, which writes the email to data/subscribers.csv. Therefore, do not treat the entire page as browser-only.
Frequently Asked Questions
How is APY different from the nominal interest rate?
The nominal rate is the stated yearly rate before compounding is taken into account. APY (annual percentage yield) reflects the effect of earning interest on interest within the year, so it is always equal to or greater than the nominal rate whenever compounding happens more than once a year.
How is APY calculated?
For a nominal annual rate r compounded n times per year, APY = (1 + r/n)^n - 1. For continuous compounding, APY = e^r - 1. The result is expressed as a percentage.
Why does APY increase with compounding frequency?
More frequent compounding means interest is credited and starts earning its own interest sooner within the year, so for the same nominal rate, daily compounding produces a higher APY than annual compounding, and continuous compounding produces the highest possible APY for a given nominal rate.
Does this tool use my actual account or bank data?
No. It only uses the nominal rate, compounding frequency, and optional deposit amount and time held that you type in. It does not fetch live interest rates, bank records, or any account data, and it is not personalized financial advice.
What happens if I enter a deposit amount?
If you enter an optional deposit amount and time held, the calculator also shows the projected ending balance and total interest earned, using the effective APY applied over the number of years entered. This is separate from the APY calculation itself, which only depends on the nominal rate and compounding frequency.