diff --git a/themes/grav/templates/forms/fields/datetime/datetime.html.twig b/themes/grav/templates/forms/fields/datetime/datetime.html.twig
index 23a71e2f..d81bc640 100644
--- a/themes/grav/templates/forms/fields/datetime/datetime.html.twig
+++ b/themes/grav/templates/forms/fields/datetime/datetime.html.twig
@@ -1,6 +1,12 @@
 {% extends "forms/field.html.twig" %}
 
 {% set default_php_dateformat = "d-m-Y H:i" %}
+
+{% if not config.system.pages.dateformat.default and value %}
+    {% if value|split('/')|count %}{% set default_php_dateformat = 'm/d/Y H:i' %}{% endif %}
+    {% if value|split('-')|first > 12 %}{% set default_php_dateformat = 'y-m-d H:i' %}{% endif %}
+{% endif %}
+
 {% set php_dateformat = config.system.pages.dateformat.default ?: default_php_dateformat %}
 {% set js_dateformat = admin.dateformatToMomentJS(php_dateformat) %}
 {% set value = (value is null ? field.default : value) %}