diff --git a/libozsh.zsh b/libozsh.zsh
index 235a444..3165882 100644
--- a/libozsh.zsh
+++ b/libozsh.zsh
@@ -51,7 +51,7 @@ function ozsh_update {
 }
 
 function ozsh_autoupdate {
-	local timediff=$(( ($(date --date="$(date)" +%s) - $(date --date="$(cat $OZSH_LASTUPDATE_FILE)" +%s) ) / (60*60*24) ))
+	local timediff=$(( ( $(strftime -r %Y-%m-%d $(date +%Y-%m-%d)) - $(strftime -r %Y-%m-%d $(cat $OZSH_LASTUPDATE_FILE)) ) / 86400 ))
 	if [ "$timediff" -ge "7" ]; then
 		vared -p 'Would you like to update ozsh? [y/N]: ' -c answer
 		if [ "$answer" = "y" ] || [ "$answer" = "Y" ]; then
@@ -68,9 +68,12 @@ function ozsh_init {
 
 	# create lastupdate file if not exist
 	if [ ! -f $OZSH_LASTUPDATE_FILE ]; then
-		echo $(date) > $OZSH_LASTUPDATE_FILE
+		echo $(date +%Y-%m-%d) > $OZSH_LASTUPDATE_FILE
 	fi
 
+	# load the datetime module
+	zmodload zsh/datetime
+
 	ozsh_autoupdate
 }