Last Updated: Nov 30, 2016
According to the Chicago Manual of Style:
An access date—that is, the self-reported date on which an author consulted a source—is of limited value: previous versions will often be unavailable to readers; authors typically consult a source any number of times over the course of days or months; and the accuracy of such dates, once recorded, cannot readily be verified by editors or publishers. Chicago does not therefore require access dates in its published citations of electronic sources unless no date of publication or revision can be determined from the source (see 14.8). For such undated sources—or for any source that seems likely to change without notice—authors are encouraged, as an additional safeguard, to archive dated copies, either as hard copy or in electronic form. Because some publishers in some disciplines—in particular, research-intensive fields such as science and medicine—do require access dates, authors should check with their publishers early on, and it never hurts to record dates of access during research. (Students are typically required to include access dates for citations of online sources in their papers.) For examples, see 14.185, 14.245, and 14.248.
See our Citation Styles guide for more information on Chicago and other citation styles.