diff --git a/app/assets/javascripts/discourse/controllers/edit-topic-auto-close.js.es6 b/app/assets/javascripts/discourse/controllers/edit-topic-auto-close.js.es6
index bb857e8d035..a6a4d0ebd18 100644
--- a/app/assets/javascripts/discourse/controllers/edit-topic-auto-close.js.es6
+++ b/app/assets/javascripts/discourse/controllers/edit-topic-auto-close.js.es6
@@ -69,7 +69,9 @@ export default Ember.Controller.extend(ModalFunctionality, {
 
   willCloseI18n: function() {
     if (this.get('model.details.auto_close_based_on_last_post')) {
-      return I18n.t('topic.auto_close_immediate', {count: this.get('model.auto_close_time')});
+      let closeDate = new Date(this.get('model.last_posted_at'));
+      let diff = Math.round((new Date() - closeDate)/(1000*60*60));
+      return I18n.t('topic.auto_close_immediate', {count: diff});
     }
   }.property('model.details.auto_close_based_on_last_post', 'model.auto_close_time')