<p>So my research mentor is going to send a supplementary rec letter, but when does it have to arrive? I know that the deadline to submit the common app is December 31st, but is it the same for supplementary rec letters?</p>
<p>yeah they prefer if you get it in by the application deadline, but they won’t penalize you if recs are received a few days afterwards. </p>
<p>[Application</a> Deadlines | Yale College Admissions](<a href=“http://admissions.yale.edu/application-deadlines]Application”>Application Deadlines | Yale College Undergraduate Admissions)</p>