Paypal has an Advanced Subscription Button that integrates a few additional hidden fields to customize the billing period and frequency.
Sample Code
<form name="_xclick" action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_xclick-subscriptions">
<input type="hidden" name="business" value="me@mybusiness.com">
<input type="hidden" name="currency_code" value="USD">
<input type="hidden" name="no_shipping" value="1">
<input type="image" src="http://www.paypal.com/en_US/i/btn/btn_subscribe_LG.gif" border="0" name="submit" alt="Make payments with PayPal - it's fast, free and secure!">
<input type="hidden" name="a3" value="50.00">
<input type="hidden" name="p3" value="3">
<input type="hidden" name="t3" value="M">
<input type="hidden" name="src" value="1">
<input type="hidden" name="sra" value="1">
</form>
The above code will create a recurring payment of $50.00 every 3 months (quarterly). The following fields affect the billing amount, period and frequency.
- a3 - amount to billed each recurrence
- p3 - number of time periods between each recurrence
- t3 - time period (D=days, W=weeks, M=months, Y=years)