This article is from the Calendars FAQ, by Claus Tondering claus@tondering.dk with numerous contributions by others.
It is 24 February!
Weird? Yes! The explanation is related to the Roman calendar and is
found in section 2.7.1.
From a numerical point of view, of course 29 February is the extra
day. But from the point of view of celebration of feast days, the
following correspondence between days in leap years and non-leap
years has traditionally been used:
Non-leap year Leap year
------------- ----------
22 February 22 February
23 February 23 February
24 February (extra day)
24 February 25 February
25 February 26 February
26 February 27 February
27 February 28 February
28 February 29 February
 
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