JavaScript and HTML form layout by Presh Talwalkar: https://mindyourdecisions.com/blog/apr-to-apy-converter/
Expository text by Richard Thripp, July 31, 2018: http://tippyfi.com/apr-to-apy-calculator/
No HTML paragraph tags are included because I rely on WordPress to automatically insert them.


<script type="text/javascript">
  function AprApyConverter(form) {
	periods = form.periods.value*1;
  		x = form.apr.value/100;
  		x = 1+x/periods;
  		x = Math.pow(x,periods);
	form.apy.value=(x-1)*100;}
function ApyAprConverter(form) {
	x=(form.apy.value/100)+1;
  		periods=1/form.periods.value;
  		x = Math.pow(x,periods);
		apr = (x-1)*form.periods.value;
  	form.apr.value=apr*100;}
</script>


<h3>APR to APY Calculator (Credit Cards)</h3>
This calculator converts an annual percentage rate (APR) to an annual percentage yield (APY). Most credit cards compound daily (365 times per year) but advertise their APR, which is misleading. The APY is the total yield to the card issuer over the course of a year (what you pay in interest). For instance, if you owe $10,000 at a 24.99% APR, with daily compounding, the APY is higher: It is 28.3787%. This means the account will accrue $2,837.87 in finance charges in one year.

<strong>How to use</strong>: Look up your credit card's APR and change the default value (24.99) if needed. Then, click CALCULATE to see your APY. You can change 365 to 12 if you are computing interest that is compounded monthly (but, credit cards usually compound daily).

<form><table border="1" cellspacing="2"><tbody>
<tr><td align="left" width="260"><strong>APR</strong> (omit % sign)</td>
<td align="left"><input type="text" name="apr" value="24.99" onclick="this.select()" width="250" /></td></tr>
<tr><td align="left" width="260">Compounded <i>x</i> times per year:</td>
<td align="left"><input type="text" name="periods" value="365" onclick="this.select()" width="250" /></td></tr>
<tr><td align="left" width="260" height="17"></td>
<td align="left"><input onclick="AprApyConverter(this.form)" type="button" value="Calculate" /></td></tr>
<tr><td align="left" width="260">The <strong>APY</strong> is:</td><td align="left"><input type="text" name="apy" readonly="readonly" width="250" /></td></tr>
</tbody></table></form>

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For more information, see <a target="_blank" href="http://tippyfi.com/2018/02/tippyfis-mission-and-the-residual-interest-caste-system-what-you-pay-for-not-paying-your-chase-freedom-credit-card-in-full-each-and-every-month/">this article on how credit card issuers maximize their profits at your expense</a>.

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<h3>APY to APR Calculator (Savings Accounts, CDs)</h3>
This calculator converts an annual percentage yield (APY) to an annual percentage rate (APR). Most savings and money market accounts compound monthly (12 times per year) and advertise their APY, which is the total yield over the course of a year. For instance, an account with $10,000 will earn $170 in a year if the APY is 1.7%. The APR is slightly lower, however.

<strong>How to use</strong>: Look up your account's APY and change the default value (1.70) if needed. Then, click CALCULATE to see your APR. You can change 12 to 365 if you are computing interest that is compounded daily, or to 4 if compounded quarterly.

<form><table border="1" cellspacing="2"><tbody>
<tr><td align="left" width="260"><strong>APY</strong> (omit % sign)</td>
<td align="left"><input type="text" name="apy" value="1.70" onclick="this.select()" width="250" /></td></tr>
<tr><td align="left" width="260">Compounded <i>x</i> times per year:</td>
<td align="left"><input type="text" name="periods" value="12" onclick="this.select()" width="250" /></td></tr>
<tr><td align="left" width="260" height="17"></td><td align="left"><input onclick="ApyAprConverter(this.form)" type="button" value="Calculate" /></td></tr>
<tr><td align="left" width="260">The <strong>APR</strong> is:</td>
<td align="left"><input type="text" name="apr" readonly="readonly" width="250" /></td></tr>
</tbody></table></form>

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<strong>Credits</strong>: JavaScript for the calculator above was written by Presh Talwalkar of <em><a target="_blank" href="https://mindyourdecisions.com/blog/apr-to-apy-converter/">Mind Your Decisions</a></em>. Richard Thripp, author of Tippyfi, adapted Talwalkar's HTML forms and wrote the expository text above. <a target="_blank" href="http://tippyfi.com/files/2018/Tippyfi-APR-to-APY-Code.txt">Click here to view/download the JavaScript and HTML forms</a>.