Hi Mike,

If you're ever unsure as to formula syntax, check out the help file and the section on formulas. This is in the Date/Time section:
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DATE(Y, M, D) or DATE(YYYY, M, D)

Description
This function returns the date value corresponding to year Y+1900, month M, and date D. Y must be in the range 0 to 199 (representing 1900-2099). It is less confusing if you use the YYYY form for the year. In this case the YYYY must be a value between 1900 and 2099

Parameters
Y year as a value between 0 and 199
YYYY year as a value between 1900 and 2099
M month
D day
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Assumig you want May 31, 2013, then the syntax is DATE(2013,5,31)