diff --git a/pref.h b/pref.h
index e59ad1c6a..29c9df2f0 100644
--- a/pref.h
+++ b/pref.h
@@ -28,6 +28,7 @@ struct preferences {
 	short profile_calc_ceiling;
 	short calc_ceiling_3m_incr;
 	short calc_all_tissues;
+	short calc_ndl_tts;
 	short gflow;
 	short gfhigh;
 	int map_provider;
diff --git a/profile.c b/profile.c
index edeb17a9d..303da6998 100644
--- a/profile.c
+++ b/profile.c
@@ -1014,6 +1014,11 @@ static void calculate_deco_information(struct dive *dive, struct divecomputer *d
 			entry->ceilings[k] = deco_allowed_depth(tolerated_by_tissue[k], surface_pressure, dive, 1);
 
 		/* calculate DECO STOP / TTS / NDL */
+
+		/* bail if we shouldn't */
+		if (!prefs.calc_ndl_tts)
+			continue;
+
 		/* We are going to mess up deco state, so store it for later restore */
 		char *cache_data = NULL;
 		cache_deco_state(tissue_tolerance, &cache_data);
diff --git a/qt-ui/mainwindow.cpp b/qt-ui/mainwindow.cpp
index c111f3926..0b3eea424 100644
--- a/qt-ui/mainwindow.cpp
+++ b/qt-ui/mainwindow.cpp
@@ -618,6 +618,7 @@ void MainWindow::readSettings()
 	GET_BOOL("dcceiling", profile_dc_ceiling);
 	GET_BOOL("calcceiling", profile_calc_ceiling);
 	GET_BOOL("calcceiling3m", calc_ceiling_3m_incr);
+	GET_BOOL("calcndltts", calc_ndl_tts);
 	GET_BOOL("calcalltissues", calc_all_tissues);
 	GET_INT("gflow", gflow);
 	GET_INT("gfhigh", gfhigh);
diff --git a/qt-ui/preferences.cpp b/qt-ui/preferences.cpp
index 4ba8739a3..f35901709 100644
--- a/qt-ui/preferences.cpp
+++ b/qt-ui/preferences.cpp
@@ -46,6 +46,8 @@ void PreferencesDialog::setUiFromPrefs()
 	ui.increment_3m->setChecked(prefs.calc_ceiling_3m_incr);
 	ui.all_tissues->setEnabled(ui.calculated_ceiling->isChecked());
 	ui.all_tissues->setChecked(prefs.calc_all_tissues);
+	ui.calc_ndl_tts->setEnabled(ui.calculated_ceiling->isChecked());
+	ui.calc_ndl_tts->setChecked(prefs.calc_ndl_tts);
 	ui.groupBox->setEnabled(ui.personalize->isChecked());
 
 	ui.gflow->setValue(prefs.gflow);
@@ -104,6 +106,7 @@ void PreferencesDialog::setPrefsFromUi()
 	SP(profile_red_ceiling, ui.red_ceiling);
 	SP(profile_calc_ceiling, ui.calculated_ceiling);
 	SP(calc_ceiling_3m_incr, ui.increment_3m);
+	SP(calc_ndl_tts, ui.calc_ndl_tts);
 	SP(calc_all_tissues, ui.all_tissues);
 	prefs.gflow = ui.gflow->value();
 	prefs.gfhigh = ui.gfhigh->value();
@@ -142,6 +145,7 @@ void PreferencesDialog::syncSettings()
 	SB("redceiling", ui.red_ceiling);
 	SB("calcceiling", ui.calculated_ceiling);
 	SB("calcceiling3m", ui.increment_3m);
+	SB("calcndltts", ui.calc_ndl_tts);
 	SB("calcalltissues", ui.all_tissues);
 	s.setValue("gflow", ui.gflow->value());
 	s.setValue("gfhigh", ui.gfhigh->value());
diff --git a/qt-ui/preferences.ui b/qt-ui/preferences.ui
index df7333837..b02e7f13a 100644
--- a/qt-ui/preferences.ui
+++ b/qt-ui/preferences.ui
@@ -711,6 +711,16 @@
                 </property>
                </widget>
               </item>
+              <item>
+               <widget class="QCheckBox" name="calc_ndl_tts">
+                <property name="enabled">
+                 <bool>false</bool>
+                </property>
+                <property name="text">
+				<string>Calculate NDL/TTS</string>
+                </property>
+               </widget>
+              </item>
              </layout>
             </item>
             <item>
@@ -997,6 +1007,22 @@
     </hint>
    </hints>
   </connection>
+  <connection>
+   <sender>calculated_ceiling</sender>
+   <signal>clicked(bool)</signal>
+   <receiver>calc_ndl_tts</receiver>
+   <slot>setEnabled(bool)</slot>
+   <hints>
+    <hint type="sourcelabel">
+     <x>298</x>
+     <y>327</y>
+    </hint>
+    <hint type="destinationlabel">
+     <x>668</x>
+     <y>327</y>
+    </hint>
+   </hints>
+  </connection>
   <connection>
    <sender>dc_reported_ceiling</sender>
    <signal>clicked(bool)</signal>
diff --git a/subsurfacestartup.c b/subsurfacestartup.c
index bc5cd42f4..8530b2f3a 100644
--- a/subsurfacestartup.c
+++ b/subsurfacestartup.c
@@ -22,6 +22,7 @@ struct preferences default_prefs = {
 	.profile_red_ceiling  = FALSE,
 	.profile_calc_ceiling = FALSE,
 	.calc_ceiling_3m_incr = FALSE,
+	.calc_ndl_tts = FALSE,
 	.gflow = 30,
 	.gfhigh = 75,
 	.font_size = 14.0,