<p>I assume you mean for tax purposes…
For taxes the date a payment or withdrawal (from a 529) is made determines what tax year it applies to. For example, if your payment for the the second semester of the 2011-2012 school year is paid in December, then it applies to your 2011 tax year. It does not matter that the payment is for the semester that will not start until 2012. If this payment is is paid in January, then is applies to your 2012 tax year.</p>