diff --git a/src/TDB2.cpp b/src/TDB2.cpp
index be3d7d83c..dc1b7762e 100644
--- a/src/TDB2.cpp
+++ b/src/TDB2.cpp
@@ -1025,203 +1025,24 @@ void TDB2::show_diff (
   Color color_red   (Context::getContext ().color () ? Context::getContext ().config.get ("color.undo.before") : "");
   Color color_green (Context::getContext ().color () ? Context::getContext ().config.get ("color.undo.after") : "");
 
+  auto before = prior == "" ? Task() : Task(prior);
+  auto after = Task(current);
+
   if (Context::getContext ().config.get ("undo.style") == "side")
   {
+    Table view = before.diffForUndoSide(after);
+
     std::cout << '\n'
               << format ("The last modification was made {1}", lastChange.toString ())
-              << '\n';
-
-    // Attributes are all there is, so figure the different attribute names
-    // between before and after.
-    Table view;
-    view.width (Context::getContext ().getWidth ());
-    view.intraPadding (2);
-    view.add ("");
-    view.add ("Prior Values");
-    view.add ("Current Values");
-    setHeaderUnderline (view);
-
-    Task after (current);
-
-    if (prior != "")
-    {
-      Task before (prior);
-
-      std::vector <std::string> beforeAtts;
-      for (auto& att : before.data_removeme ())
-        beforeAtts.push_back (att.first);
-
-      std::vector <std::string> afterAtts;
-      for (auto& att : after.data_removeme ())
-        afterAtts.push_back (att.first);
-
-      std::vector <std::string> beforeOnly;
-      std::vector <std::string> afterOnly;
-      listDiff (beforeAtts, afterAtts, beforeOnly, afterOnly);
-
-      int row;
-      for (auto& name : beforeOnly)
-      {
-        row = view.addRow ();
-        view.set (row, 0, name);
-        view.set (row, 1, renderAttribute (name, before.get (name)), color_red);
-      }
-
-      for (auto& att : before.data_removeme ())
-      {
-        std::string priorValue   = before.get (att.first);
-        std::string currentValue = after.get  (att.first);
-
-        if (currentValue != "")
-        {
-          row = view.addRow ();
-          view.set (row, 0, att.first);
-          view.set (row, 1, renderAttribute (att.first, priorValue),
-                    (priorValue != currentValue ? color_red : Color ()));
-          view.set (row, 2, renderAttribute (att.first, currentValue),
-                    (priorValue != currentValue ? color_green : Color ()));
-        }
-      }
-
-      for (auto& name : afterOnly)
-      {
-        row = view.addRow ();
-        view.set (row, 0, name);
-        view.set (row, 2, renderAttribute (name, after.get (name)), color_green);
-      }
-    }
-    else
-    {
-      int row;
-      for (auto& att : after.data_removeme ())
-      {
-        row = view.addRow ();
-        view.set (row, 0, att.first);
-        view.set (row, 2, renderAttribute (att.first, after.get (att.first)), color_green);
-      }
-    }
-
-    std::cout << '\n'
+              << '\n'
+              << '\n'
               << view.render ()
               << '\n';
   }
 
-  // This style looks like this:
-  //  --- before    2009-07-04 00:00:25.000000000 +0200
-  //  +++ after    2009-07-04 00:00:45.000000000 +0200
-  //
-  // - name: old           // att deleted
-  // + name:
-  //
-  // - name: old           // att changed
-  // + name: new
-  //
-  // - name:
-  // + name: new           // att added
-  //
   else if (Context::getContext ().config.get ("undo.style") == "diff")
   {
-    // Create reference tasks.
-    Task before;
-    if (prior != "")
-      before.parse (prior);
-
-    Task after (current);
-
-    // Generate table header.
-    Table view;
-    view.width (Context::getContext ().getWidth ());
-    view.intraPadding (2);
-    view.add ("");
-    view.add ("");
-
-    int row = view.addRow ();
-    view.set (row, 0, "--- previous state", color_red);
-    view.set (row, 1, "Undo will restore this state", color_red);
-
-    row = view.addRow ();
-    view.set (row, 0, "+++ current state ", color_green);
-    view.set (row, 1, format ("Change made {1}",
-                              lastChange.toString (Context::getContext ().config.get ("dateformat"))),
-                      color_green);
-
-    view.addRow ();
-
-    // Add rows to table showing diffs.
-    std::vector <std::string> all = Context::getContext ().getColumns ();
-
-    // Now factor in the annotation attributes.
-    for (auto& it : before.data_removeme ())
-      if (it.first.substr (0, 11) == "annotation_")
-        all.push_back (it.first);
-
-    for (auto& it : after.data_removeme ())
-      if (it.first.substr (0, 11) == "annotation_")
-        all.push_back (it.first);
-
-    // Now render all the attributes.
-    std::sort (all.begin (), all.end ());
-
-    std::string before_att;
-    std::string after_att;
-    std::string last_att;
-    for (auto& a : all)
-    {
-      if (a != last_att)  // Skip duplicates.
-      {
-        last_att = a;
-
-        before_att = before.get (a);
-        after_att  = after.get (a);
-
-        // Don't report different uuid.
-        // Show nothing if values are the unchanged.
-        if (a == "uuid" ||
-            before_att == after_att)
-        {
-          // Show nothing - no point displaying that which did not change.
-
-          // row = view.addRow ();
-          // view.set (row, 0, *a + ":");
-          // view.set (row, 1, before_att);
-        }
-
-        // Attribute deleted.
-        else if (before_att != "" && after_att == "")
-        {
-          row = view.addRow ();
-          view.set (row, 0, '-' + a + ':', color_red);
-          view.set (row, 1, before_att, color_red);
-
-          row = view.addRow ();
-          view.set (row, 0, '+' + a + ':', color_green);
-        }
-
-        // Attribute added.
-        else if (before_att == "" && after_att != "")
-        {
-          row = view.addRow ();
-          view.set (row, 0, '-' + a + ':', color_red);
-
-          row = view.addRow ();
-          view.set (row, 0, '+' + a + ':', color_green);
-          view.set (row, 1, after_att, color_green);
-        }
-
-        // Attribute changed.
-        else
-        {
-          row = view.addRow ();
-          view.set (row, 0, '-' + a + ':', color_red);
-          view.set (row, 1, before_att, color_red);
-
-          row = view.addRow ();
-          view.set (row, 0, '+' + a + ':', color_green);
-          view.set (row, 1, after_att, color_green);
-        }
-      }
-    }
-
+    Table view = before.diffForUndoPatch(after, lastChange);
     std::cout << '\n'
               << view.render ()
               << '\n';
diff --git a/src/Task.cpp b/src/Task.cpp
index f0ddf833a..dd48514df 100644
--- a/src/Task.cpp
+++ b/src/Task.cpp
@@ -2425,7 +2425,8 @@ void Task::modify (modType type, bool text_required /* = false */)
 #endif
 
 ////////////////////////////////////////////////////////////////////////////////
-// Compare this task to another and summarize the differences for display
+// Compare this task to another and summarize the differences for display, in
+// the future tense ("Foo will be set to ..").
 std::string Task::diff (const Task& after) const
 {
   // Attributes are all there is, so figure the different attribute names
@@ -2670,3 +2671,206 @@ std::string Task::diffForInfo (
 }
 
 ////////////////////////////////////////////////////////////////////////////////
+// Similar to diff, but formatted as a side-by-side table for an Undo preview
+Table Task::diffForUndoSide (
+  const Task& after) const
+{
+  // Set the colors.
+  Color color_red   (Context::getContext ().color () ? Context::getContext ().config.get ("color.undo.before") : "");
+  Color color_green (Context::getContext ().color () ? Context::getContext ().config.get ("color.undo.after") : "");
+
+  // Attributes are all there is, so figure the different attribute names
+  // between before and after.
+  Table view;
+  view.width (Context::getContext ().getWidth ());
+  view.intraPadding (2);
+  view.add ("");
+  view.add ("Prior Values");
+  view.add ("Current Values");
+  setHeaderUnderline (view);
+
+  if (!is_empty ())
+  {
+    const Task &before = *this;
+
+    std::vector <std::string> beforeAtts;
+    for (auto& att : before.data)
+      beforeAtts.push_back (att.first);
+
+    std::vector <std::string> afterAtts;
+    for (auto& att : after.data)
+      afterAtts.push_back (att.first);
+
+    std::vector <std::string> beforeOnly;
+    std::vector <std::string> afterOnly;
+    listDiff (beforeAtts, afterAtts, beforeOnly, afterOnly);
+
+    int row;
+    for (auto& name : beforeOnly)
+    {
+      row = view.addRow ();
+      view.set (row, 0, name);
+      view.set (row, 1, renderAttribute (name, before.get (name)), color_red);
+    }
+
+    for (auto& att : before.data)
+    {
+      std::string priorValue   = before.get (att.first);
+      std::string currentValue = after.get  (att.first);
+
+      if (currentValue != "")
+      {
+        row = view.addRow ();
+        view.set (row, 0, att.first);
+        view.set (row, 1, renderAttribute (att.first, priorValue),
+                  (priorValue != currentValue ? color_red : Color ()));
+        view.set (row, 2, renderAttribute (att.first, currentValue),
+                  (priorValue != currentValue ? color_green : Color ()));
+      }
+    }
+
+    for (auto& name : afterOnly)
+    {
+      row = view.addRow ();
+      view.set (row, 0, name);
+      view.set (row, 2, renderAttribute (name, after.get (name)), color_green);
+    }
+  }
+  else
+  {
+    int row;
+    for (auto& att : after.data)
+    {
+      row = view.addRow ();
+      view.set (row, 0, att.first);
+      view.set (row, 2, renderAttribute (att.first, after.get (att.first)), color_green);
+    }
+  }
+
+  return view;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Similar to diff, but formatted as a diff for an Undo preview
+Table Task::diffForUndoPatch (
+  const Task& after,
+  const Datetime& lastChange) const
+{
+  // This style looks like this:
+  //  --- before    2009-07-04 00:00:25.000000000 +0200
+  //  +++ after    2009-07-04 00:00:45.000000000 +0200
+  //
+  // - name: old           // att deleted
+  // + name:
+  //
+  // - name: old           // att changed
+  // + name: new
+  //
+  // - name:
+  // + name: new           // att added
+  //
+
+  // Set the colors.
+  Color color_red   (Context::getContext ().color () ? Context::getContext ().config.get ("color.undo.before") : "");
+  Color color_green (Context::getContext ().color () ? Context::getContext ().config.get ("color.undo.after") : "");
+
+  const Task &before = *this;
+
+  // Generate table header.
+  Table view;
+  view.width (Context::getContext ().getWidth ());
+  view.intraPadding (2);
+  view.add ("");
+  view.add ("");
+
+  int row = view.addRow ();
+  view.set (row, 0, "--- previous state", color_red);
+  view.set (row, 1, "Undo will restore this state", color_red);
+
+  row = view.addRow ();
+  view.set (row, 0, "+++ current state ", color_green);
+  view.set (row, 1, format ("Change made {1}",
+                            lastChange.toString (Context::getContext ().config.get ("dateformat"))),
+                    color_green);
+
+  view.addRow ();
+
+  // Add rows to table showing diffs.
+  std::vector <std::string> all = Context::getContext ().getColumns ();
+
+  // Now factor in the annotation attributes.
+  for (auto& it : before.data)
+    if (it.first.substr (0, 11) == "annotation_")
+      all.push_back (it.first);
+
+  for (auto& it : after.data)
+    if (it.first.substr (0, 11) == "annotation_")
+      all.push_back (it.first);
+
+  // Now render all the attributes.
+  std::sort (all.begin (), all.end ());
+
+  std::string before_att;
+  std::string after_att;
+  std::string last_att;
+  for (auto& a : all)
+  {
+    if (a != last_att)  // Skip duplicates.
+    {
+      last_att = a;
+
+      before_att = before.get (a);
+      after_att  = after.get (a);
+
+      // Don't report different uuid.
+      // Show nothing if values are the unchanged.
+      if (a == "uuid" ||
+          before_att == after_att)
+      {
+        // Show nothing - no point displaying that which did not change.
+
+        // row = view.addRow ();
+        // view.set (row, 0, *a + ":");
+        // view.set (row, 1, before_att);
+      }
+
+      // Attribute deleted.
+      else if (before_att != "" && after_att == "")
+      {
+        row = view.addRow ();
+        view.set (row, 0, '-' + a + ':', color_red);
+        view.set (row, 1, before_att, color_red);
+
+        row = view.addRow ();
+        view.set (row, 0, '+' + a + ':', color_green);
+      }
+
+      // Attribute added.
+      else if (before_att == "" && after_att != "")
+      {
+        row = view.addRow ();
+        view.set (row, 0, '-' + a + ':', color_red);
+
+        row = view.addRow ();
+        view.set (row, 0, '+' + a + ':', color_green);
+        view.set (row, 1, after_att, color_green);
+      }
+
+      // Attribute changed.
+      else
+      {
+        row = view.addRow ();
+        view.set (row, 0, '-' + a + ':', color_red);
+        view.set (row, 1, before_att, color_red);
+
+        row = view.addRow ();
+        view.set (row, 0, '+' + a + ':', color_green);
+        view.set (row, 1, after_att, color_green);
+      }
+    }
+  }
+
+  return view;
+}
+
+////////////////////////////////////////////////////////////////////////////////
diff --git a/src/Task.h b/src/Task.h
index 13ec396fa..c3a6259f1 100644
--- a/src/Task.h
+++ b/src/Task.h
@@ -33,6 +33,8 @@
 #include <stdio.h>
 #include <time.h>
 #include <JSON.h>
+#include <Table.h>
+#include <Datetime.h>
 
 class Task
 {
@@ -173,6 +175,8 @@ public:
 
   std::string diff (const Task& after) const;
   std::string diffForInfo (const Task& after, const std::string& dateformat, long& last_timestamp, const long current_timestamp) const; 
+  Table diffForUndoSide (const Task& after) const;
+  Table diffForUndoPatch (const Task& after, const Datetime& lastChange) const;
 
 private:
   int determineVersion (const std::string&);