title: How does Stripe's prorating work?
body: <p>From Stripe's documentation under updating a user's subscription plan:</p>
  
  <blockquote>
    <p>By default, we prorate subscription changes. For example, if a customer signs up on May 1 for a $10 plan, she'll be billed $10 immediately. If she then switches to a $20 plan on May 15, on June 1 she'll be billed $25 ($20 for a renewal of her subscription and a $5 prorating adjustment for the previous month).</p>
  </blockquote>
  
  <p>Shouldn't the charge on June 1st be $30; $20 for the renewal and $10 (half of $20 because half of May) for the previous month? Did Stripe get their calculations confused, or am I dead wrong on how prorating works?</p>