diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -54,6 +54,7 @@
     pycompat,
     urllibcompat,
 )
+from .utils import dateutil
 
 base85 = policy.importmod(r'base85')
 osutil = policy.importmod(r'osutil')
@@ -530,48 +531,6 @@
     if n == 4:
         return (vints[0], vints[1], vints[2], extra)
 
-# used by parsedate
-defaultdateformats = (
-    '%Y-%m-%dT%H:%M:%S', # the 'real' ISO8601
-    '%Y-%m-%dT%H:%M',    #   without seconds
-    '%Y-%m-%dT%H%M%S',   # another awful but legal variant without :
-    '%Y-%m-%dT%H%M',     #   without seconds
-    '%Y-%m-%d %H:%M:%S', # our common legal variant
-    '%Y-%m-%d %H:%M',    #   without seconds
-    '%Y-%m-%d %H%M%S',   # without :
-    '%Y-%m-%d %H%M',     #   without seconds
-    '%Y-%m-%d %I:%M:%S%p',
-    '%Y-%m-%d %H:%M',
-    '%Y-%m-%d %I:%M%p',
-    '%Y-%m-%d',
-    '%m-%d',
-    '%m/%d',
-    '%m/%d/%y',
-    '%m/%d/%Y',
-    '%a %b %d %H:%M:%S %Y',
-    '%a %b %d %I:%M:%S%p %Y',
-    '%a, %d %b %Y %H:%M:%S',        #  GNU coreutils "/bin/date --rfc-2822"
-    '%b %d %H:%M:%S %Y',
-    '%b %d %I:%M:%S%p %Y',
-    '%b %d %H:%M:%S',
-    '%b %d %I:%M:%S%p',
-    '%b %d %H:%M',
-    '%b %d %I:%M%p',
-    '%b %d %Y',
-    '%b %d',
-    '%H:%M:%S',
-    '%I:%M:%S%p',
-    '%H:%M',
-    '%I:%M%p',
-)
-
-extendeddateformats = defaultdateformats + (
-    "%Y",
-    "%Y-%m",
-    "%b",
-    "%b %Y",
-    )
-
 def cachefunc(func):
     '''cache the result of function calls'''
     # XXX doesn't handle keywords args
@@ -3944,3 +3903,12 @@
         if not (byte & 0x80):
             return result
         shift += 7
+
+###
+# Deprecation warnings for util.py splitting
+###
+
+defaultdateformats = dateutil.defaultdateformats
+
+extendeddateformats = dateutil.extendeddateformats
+
diff --git a/mercurial/utils/dateutil.py b/mercurial/utils/dateutil.py
--- a/mercurial/utils/dateutil.py
+++ b/mercurial/utils/dateutil.py
@@ -6,3 +6,45 @@
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import, print_function
+
+# used by parsedate
+defaultdateformats = (
+    '%Y-%m-%dT%H:%M:%S', # the 'real' ISO8601
+    '%Y-%m-%dT%H:%M',    #   without seconds
+    '%Y-%m-%dT%H%M%S',   # another awful but legal variant without :
+    '%Y-%m-%dT%H%M',     #   without seconds
+    '%Y-%m-%d %H:%M:%S', # our common legal variant
+    '%Y-%m-%d %H:%M',    #   without seconds
+    '%Y-%m-%d %H%M%S',   # without :
+    '%Y-%m-%d %H%M',     #   without seconds
+    '%Y-%m-%d %I:%M:%S%p',
+    '%Y-%m-%d %H:%M',
+    '%Y-%m-%d %I:%M%p',
+    '%Y-%m-%d',
+    '%m-%d',
+    '%m/%d',
+    '%m/%d/%y',
+    '%m/%d/%Y',
+    '%a %b %d %H:%M:%S %Y',
+    '%a %b %d %I:%M:%S%p %Y',
+    '%a, %d %b %Y %H:%M:%S',        #  GNU coreutils "/bin/date --rfc-2822"
+    '%b %d %H:%M:%S %Y',
+    '%b %d %I:%M:%S%p %Y',
+    '%b %d %H:%M:%S',
+    '%b %d %I:%M:%S%p',
+    '%b %d %H:%M',
+    '%b %d %I:%M%p',
+    '%b %d %Y',
+    '%b %d',
+    '%H:%M:%S',
+    '%I:%M:%S%p',
+    '%H:%M',
+    '%I:%M%p',
+)
+
+extendeddateformats = defaultdateformats + (
+    "%Y",
+    "%Y-%m",
+    "%b",
+    "%b %Y",
+)