diff --git a/db/migrate/20240923131205_add_child_birthday_to_usr.rb b/db/migrate/20240923131205_add_child_birthday_to_usr.rb
index e97bf92..a020225 100644
--- a/db/migrate/20240923131205_add_child_birthday_to_usr.rb
+++ b/db/migrate/20240923131205_add_child_birthday_to_usr.rb
@@ -3,7 +3,7 @@ def change
     add_column :users, :child_birthday, :date
 
     User.find_each do |user|
-      user.update(child_birthday: user.created_at - 18.months)
+      user.update(child_birthday: Time.now - user.child_age.months)
     end
 
     remove_column :users, :child_age, :date