diff --git a/Gemfile b/Gemfile
index 51afecde..a1a0e62f 100644
--- a/Gemfile
+++ b/Gemfile
@@ -36,6 +36,7 @@ gem 'bootstrap3-datetimepicker-rails' # for the datetime widget
 gem 'bootstrap-toggle-rails' # for toggle buttons instead of checkboxes
 
 gem 'momentjs-rails', '>= 2.9.0' # needed for human-friendly textual dates
+gem 'moment_timezone-rails'
 gem 'font-awesome-rails'
 
 gem 'addressable'
diff --git a/Gemfile.lock b/Gemfile.lock
index 41e874ab..bc20d9f4 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -168,6 +168,7 @@ GEM
       builder
       minitest (>= 5.0)
       ruby-progressbar
+    moment_timezone-rails (0.5.0)
     momentjs-rails (2.20.1)
       railties (>= 3.1)
     net-ldap (0.16.2)
@@ -330,6 +331,7 @@ DEPENDENCIES
   launchy
   listen
   minitest-reporters
+  moment_timezone-rails
   momentjs-rails (>= 2.9.0)
   passenger (>= 5.0.25)
   pg
diff --git a/app/assets/javascripts/application.js b/app/assets/javascripts/application.js
index a306279c..8e243976 100644
--- a/app/assets/javascripts/application.js
+++ b/app/assets/javascripts/application.js
@@ -21,6 +21,7 @@
 //= require jquery.keyDecoder
 //= require cocoon
 //= require moment
+//= require moment-timezone-with-data
 //= require bootstrap-sprockets
 //= require bootstrap-datetimepicker
 //= require bootstrap.treeview
@@ -172,6 +173,24 @@ function makeFriendlyDate(str, showTime) {
   }
 }
 
+// convert human-readable datetimes to ISO8601 times, including timezone
+function makeDatesIso8601($dates) {
+  var savedDates = [];
+  $dates.each(function(index, dtp) {
+    var $dtp = $(dtp);
+    savedDates[index] = $dtp.val();
+    $dtp.val($dtp.data("DateTimePicker").date().format());
+  });
+  return savedDates;
+}
+
+function restoreDatesFromIso8601($dates, savedDates) {
+  $dates.each(function(index, dtp) {
+    $(dtp).val(savedDates[index]);
+  });
+}
+
+
 function activate_file_picker($e) {
   $e.find(".custom-file").change(function() {
     var label = $(this).val().replace(/\\/g, '/').replace(/.*\//, '');
diff --git a/app/assets/javascripts/assignments.js b/app/assets/javascripts/assignments.js
index 044ad413..1ece2b80 100644
--- a/app/assets/javascripts/assignments.js
+++ b/app/assets/javascripts/assignments.js
@@ -140,7 +140,8 @@
   function init_datetime() {
     $('.datetime-picker').datetimepicker({
       sideBySide: true,
-      format: "YYYY/MM/DD h:mm A",
+      format: "YYYY/MM/DD h:mm A z",
+      timeZone: moment.tz.guess(),
       defaultDate: undefined
     });
   }
@@ -240,6 +241,7 @@
           return false;
         }
       }
+      makeDatesIso8601($(".datetime-picker"));
       return true;
     });
 
diff --git a/app/models/course.rb b/app/models/course.rb
index 1f402970..62c19d52 100644
--- a/app/models/course.rb
+++ b/app/models/course.rb
@@ -205,6 +205,7 @@ def score_summary(for_students = nil)
           if sub.score.nil?
             if assns[sub.assignment_id].extra_credit
               extra_adjust += assns[sub.assignment_id].points_available
+              extra_avail  -= assns[sub.assignment_id].points_available # Don't double-count
             else
               adjust += assns[sub.assignment_id].points_available
             end
@@ -223,10 +224,10 @@ def score_summary(for_students = nil)
           unsubs += o.points_available
         end
       end
-      max = min + remaining + extra_adjust + adjust + unsubs
+      max = min + remaining + extra_adjust + adjust + unsubs + extra_avail
       {s: s, dropped: dropped,
        min: min * (100.0 / total_points), cur: cur * (100.0 / total_points), max: max * (100.0 / total_points),
-       pending: adjust + extra_adjust, pending_names: pending_names,
+       pending: adjust + extra_adjust + extra_avail, pending_names: pending_names,
        unsub: unsubs, unsub_names: unsub_names,
        remaining: remaining, used: used}
     end
diff --git a/app/views/individual_extensions/_edit.js.erb b/app/views/individual_extensions/_edit.js.erb
index 1c060d7a..2e03a258 100644
--- a/app/views/individual_extensions/_edit.js.erb
+++ b/app/views/individual_extensions/_edit.js.erb
@@ -7,7 +7,8 @@ $(function() {
   $initialFilled.closest("tr").find("button.revoke").removeClass("hidden");
   $('.datetime-picker').datetimepicker({
     sideBySide: true,
-    format: "YYYY/MM/DD h:mm A",
+    format: "YYYY/MM/DD h:mm A z",
+    timeZone: moment.tz.guess(),
     defaultDate: undefined
   });
   $("form").map(function() {
@@ -24,11 +25,15 @@ $(function() {
     var $valuesToSubmit = $row.find("form");
     var $check = $row.find("#success_" + $valuesToSubmit[0].id);
     var $fail  = $row.find("#failure_" + $valuesToSubmit[0].id);
+    var $dates = $row.find(".datetime-picker");
+    var savedDates = makeDatesIso8601($dates);
+    var data = $valuesToSubmit.serialize();
+    restoreDatesFromIso8601($dates, savedDates);
     debugger
     $.ajax({
       type: "PATCH",
       url: "<%= patch_course_assignment_extensions_path(@course, @assignment) %>",
-      data: $valuesToSubmit.serialize(),
+      data: data,
       dataType: "JSON",
       timeout: 500
     }).done(function(json) {
@@ -55,10 +60,14 @@ $(function() {
     var $valuesToSubmit = $row.find("form");
     var $check = $row.find("#success_" + $valuesToSubmit[0].id);
     var $fail  = $row.find("#failure_" + $valuesToSubmit[0].id);
+    var $dates = $row.find(".datetime-picker");
+    var savedDates = makeDatesIso8601($dates);
+    var data = $valuesToSubmit.serialize();
+    restoreDatesFromIso8601($dates, savedDates);
     $.ajax({
       type: "DELETE",
       url: "<%= delete_course_assignment_extensions_path(@course, @assignment) %>",
-      data: $valuesToSubmit.serialize(),
+      data: data,
       dataType: "JSON",
       timeout: 500
     }).done(function(json) {
diff --git a/app/views/submissions/_new_common.html.erb b/app/views/submissions/_new_common.html.erb
index 120feafd..551103c6 100644
--- a/app/views/submissions/_new_common.html.erb
+++ b/app/views/submissions/_new_common.html.erb
@@ -57,7 +57,7 @@
         <div class="col-sm-6">
           <p>If lateness is not ignored, this <%= type[:noun] %> should claim to
             have been submitted at:</p>
-          <%= f.text_field :created_at, class: 'form-control', disabled: "disabled" %>
+          <%= f.text_field :created_at, class: 'form-control datetime-picker', disabled: "disabled" %>
         </div>
         <% end %>
         <div class="col-sm-6" style="padding-top: 1em;">
@@ -70,7 +70,8 @@
           $(function () {
             $('#submission_created_at').datetimepicker({
               sideBySide: true,
-              format: "YYYY/MM/DD h:mm A",
+              format: "YYYY/MM/DD h:mm A z",
+              timeZone: moment.tz.guess(),
               minDate: "<%= @course.created_at.beginning_of_day.iso8601 %>",
               <% if @course.created_at < DateTime.current %>
               defaultDate: "<%= DateTime.current.iso8601 %>"
diff --git a/app/views/submissions/new_codereview.html.erb b/app/views/submissions/new_codereview.html.erb
index a1dbf659..57f6e45a 100644
--- a/app/views/submissions/new_codereview.html.erb
+++ b/app/views/submissions/new_codereview.html.erb
@@ -180,7 +180,11 @@
     warning.find("h3").removeClass("hidden");
   }, Math.max(deadline - now, 0));
   $("form").submit(function(e) {
-    return ensureValidNumericInputOnSubmit(e, "input.numeric:not([disabled])");
+    var num = ensureValidNumericInputOnSubmit(e, "input.numeric:not([disabled])");
+    if (num) {
+      makeDatesIso8601($(".datetime-picker"));
+    }
+    return num;
   });
 </script>
 <% end %><%# content-for %>
diff --git a/app/views/submissions/new_files.html.erb b/app/views/submissions/new_files.html.erb
index d0d17570..54bf9bdf 100644
--- a/app/views/submissions/new_files.html.erb
+++ b/app/views/submissions/new_files.html.erb
@@ -97,6 +97,9 @@
   $("form").submit(function(e) {
     var num = ensureValidNumericInputOnSubmit(e, "span.spinner > input");
     var files = ensureFilesPresentOnSubmit(e);
+    if (num && files) {
+      makeDatesIso8601($(".datetime-picker"));
+    }
     return num && files;
   });
 </script>
diff --git a/app/views/submissions/new_questions.html.erb b/app/views/submissions/new_questions.html.erb
index 209d6adc..acdf6b64 100644
--- a/app/views/submissions/new_questions.html.erb
+++ b/app/views/submissions/new_questions.html.erb
@@ -108,7 +108,11 @@
     warning.find("h3").removeClass("hidden");
   }, Math.max(deadline - now, 0));
   $("form").submit(function(e) {
-    return ensureValidNumericInputOnSubmit(e, "input.numeric:not([disabled])");
+    var num = ensureValidNumericInputOnSubmit(e, "input.numeric:not([disabled])");
+    if (num) {
+      makeDatesIso8601($(".datetime-picker"));
+    }
+    return num;
   });
 </script>
 <% end %>
diff --git a/test/integration/submissions_test.rb b/test/integration/submissions_test.rb
index 658d7498..e336b0f2 100644
--- a/test/integration/submissions_test.rb
+++ b/test/integration/submissions_test.rb
@@ -161,10 +161,10 @@ def clean(summary)
     @as3.reload # needed for the lateness config
     @summary = clean(@cs101.score_summary(@john))
     assert_equal(@summary[@john.id],
-                 {dropped: nil, min: 7.5, cur: 75.0, max: 97.5,
+                 {dropped: nil, min: 7.5, cur: 75.0, max: 102.5,
                   pending: 0.0, pending_names: [], unsub: 0.0, unsub_names: [],
                   remaining: 90.0},
-                "After creating an extra credit assignment, but not submitting, nothing should change in the grades")
+                "After creating an extra credit assignment, but not submitting, max goes up by the available e.c.")
 
     @sub3 = create(:submission, user: @john, assignment: @as3, created_at: Time.now - 2.days)
     @sub3.set_used_sub!