<p>Why don't people just check the pertinent web site? Sigh ...</p>
<p>OK, just this once and because you are new, here you go. I looked it up for you: <a href="http://www.sat.org/student/testing/sat/testday/standby.html%5B/url%5D">http://www.sat.org/student/testing/sat/testday/standby.html</a></p>
<p>You can still sign up for December testing, though. <a href="http://www.sat.org/student/testing/sat/calenfees.html%5B/url%5D">http://www.sat.org/student/testing/sat/calenfees.html</a></p>
<p>The disadvantage of standby, in addition to the added fee, is you might not get in. (Also, if you read the link, you will see that you can't take a listening test on standby.) If I were in your shoes, I would just sign up for December. Even if you are applying ED/EA, you may find your school(s) will accept December testing. Many do. But if this is your situation, please check the school's web site. It will tell you for sure.</p>