diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -2649,7 +2649,8 @@
     'PhabricatorChangeParserTestCase' => 'applications/repository/worker/__tests__/PhabricatorChangeParserTestCase.php',
     'PhabricatorChangesetCachePurger' => 'applications/cache/purger/PhabricatorChangesetCachePurger.php',
     'PhabricatorChangesetResponse' => 'infrastructure/diff/PhabricatorChangesetResponse.php',
-    'PhabricatorChartFunction' => 'applications/fact/function/PhabricatorChartFunction.php',
+    'PhabricatorChartAxis' => 'applications/fact/chart/PhabricatorChartAxis.php',
+    'PhabricatorChartFunction' => 'applications/fact/chart/PhabricatorChartFunction.php',
     'PhabricatorChatLogApplication' => 'applications/chatlog/application/PhabricatorChatLogApplication.php',
     'PhabricatorChatLogChannel' => 'applications/chatlog/storage/PhabricatorChatLogChannel.php',
     'PhabricatorChatLogChannelListController' => 'applications/chatlog/controller/PhabricatorChatLogChannelListController.php',
@@ -3204,7 +3205,7 @@
     'PhabricatorFactApplication' => 'applications/fact/application/PhabricatorFactApplication.php',
     'PhabricatorFactChart' => 'applications/fact/storage/PhabricatorFactChart.php',
     'PhabricatorFactChartController' => 'applications/fact/controller/PhabricatorFactChartController.php',
-    'PhabricatorFactChartFunction' => 'applications/fact/function/PhabricatorFactChartFunction.php',
+    'PhabricatorFactChartFunction' => 'applications/fact/chart/PhabricatorFactChartFunction.php',
     'PhabricatorFactController' => 'applications/fact/controller/PhabricatorFactController.php',
     'PhabricatorFactCursor' => 'applications/fact/storage/PhabricatorFactCursor.php',
     'PhabricatorFactDAO' => 'applications/fact/storage/PhabricatorFactDAO.php',
@@ -8621,6 +8622,7 @@
     'PhabricatorChangeParserTestCase' => 'PhabricatorWorkingCopyTestCase',
     'PhabricatorChangesetCachePurger' => 'PhabricatorCachePurger',
     'PhabricatorChangesetResponse' => 'AphrontProxyResponse',
+    'PhabricatorChartAxis' => 'Phobject',
     'PhabricatorChartFunction' => 'Phobject',
     'PhabricatorChatLogApplication' => 'PhabricatorApplication',
     'PhabricatorChatLogChannel' => array(
diff --git a/src/applications/fact/chart/PhabricatorChartAxis.php b/src/applications/fact/chart/PhabricatorChartAxis.php
new file mode 100644
--- /dev/null
+++ b/src/applications/fact/chart/PhabricatorChartAxis.php
@@ -0,0 +1,27 @@
+<?php
+
+final class PhabricatorChartAxis
+  extends Phobject {
+
+  private $minimumValue;
+  private $maximumValue;
+
+  public function setMinimumValue($minimum_value) {
+    $this->minimumValue = $minimum_value;
+    return $this;
+  }
+
+  public function getMinimumValue() {
+    return $this->minimumValue;
+  }
+
+  public function setMaximumValue($maximum_value) {
+    $this->maximumValue = $maximum_value;
+    return $this;
+  }
+
+  public function getMaximumValue() {
+    return $this->maximumValue;
+  }
+
+}
diff --git a/src/applications/fact/function/PhabricatorChartFunction.php b/src/applications/fact/chart/PhabricatorChartFunction.php
rename from src/applications/fact/function/PhabricatorChartFunction.php
rename to src/applications/fact/chart/PhabricatorChartFunction.php
--- a/src/applications/fact/function/PhabricatorChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorChartFunction.php
@@ -3,6 +3,10 @@
 abstract class PhabricatorChartFunction
   extends Phobject {
 
+  private $xAxis;
+  private $yAxis;
+  private $limit;
+
   final public function getFunctionKey() {
     return $this->getPhobjectClassConstant('FUNCTIONKEY', 32);
   }
@@ -21,4 +25,22 @@
 
   abstract protected function newArguments(array $arguments);
 
+  final public function setXAxis(PhabricatorChartAxis $x_axis) {
+    $this->xAxis = $x_axis;
+    return $this;
+  }
+
+  final public function getXAxis() {
+    return $this->xAxis;
+  }
+
+  final public function setYAxis(PhabricatorChartAxis $y_axis) {
+    $this->yAxis = $y_axis;
+    return $this;
+  }
+
+  final public function getYAxis() {
+    return $this->yAxis;
+  }
+
 }
diff --git a/src/applications/fact/function/PhabricatorFactChartFunction.php b/src/applications/fact/chart/PhabricatorFactChartFunction.php
rename from src/applications/fact/function/PhabricatorFactChartFunction.php
rename to src/applications/fact/chart/PhabricatorFactChartFunction.php
--- a/src/applications/fact/function/PhabricatorFactChartFunction.php
+++ b/src/applications/fact/chart/PhabricatorFactChartFunction.php
@@ -83,6 +83,26 @@
       return array();
     }
 
+    $axis = $this->getXAxis();
+    $x_min = $axis->getMinimumValue();
+    $x_max = $axis->getMaximumValue();
+
+    if ($x_min !== null) {
+      foreach ($points as $key => $point) {
+        if ($point['x'] < $x_min) {
+          unset($points[$key]);
+        }
+      }
+    }
+
+    if ($x_max !== null) {
+      foreach ($points as $key => $point) {
+        if ($point['x'] > $x_max) {
+          unset($points[$key]);
+        }
+      }
+    }
+
     // If we have too many data points, throw away some of the data.
     $count = count($points);
     if ($count > $limit) {
@@ -99,4 +119,15 @@
     return $points;
   }
 
+  public function hasDomain() {
+    return true;
+  }
+
+  public function getDomain() {
+    // TODO: We can examine the data to fit a better domain.
+
+    $now = PhabricatorTime::getNow();
+    return array($now - phutil_units('90 days in seconds'), $now);
+  }
+
 }
diff --git a/src/applications/fact/controller/PhabricatorFactChartController.php b/src/applications/fact/controller/PhabricatorFactChartController.php
--- a/src/applications/fact/controller/PhabricatorFactChartController.php
+++ b/src/applications/fact/controller/PhabricatorFactChartController.php
@@ -24,8 +24,16 @@
       return $this->newChartResponse();
     }
 
+    list($domain_min, $domain_max) = $this->getDomain($functions);
+
+    $axis = id(new PhabricatorChartAxis())
+      ->setMinimumValue($domain_min)
+      ->setMaximumValue($domain_max);
+
     $datasets = array();
     foreach ($functions as $function) {
+      $function->setXAxis($axis);
+
       $function->loadData();
 
       $points = $function->getDatapoints(2000);
@@ -45,10 +53,9 @@
       );
     }
 
+
     $y_min = 0;
     $y_max = 0;
-    $x_min = null;
-    $x_max = 0;
     foreach ($datasets as $dataset) {
       if (!$dataset['y']) {
         continue;
@@ -56,20 +63,12 @@
 
       $y_min = min($y_min, min($dataset['y']));
       $y_max = max($y_max, max($dataset['y']));
-
-      if ($x_min === null) {
-        $x_min = min($dataset['x']);
-      } else {
-        $x_min = min($x_min, min($dataset['x']));
-      }
-
-      $x_max = max($x_max, max($dataset['x']));
     }
 
     $chart_data = array(
       'datasets' => $datasets,
-      'xMin' => $x_min,
-      'xMax' => $x_max,
+      'xMin' => $domain_min,
+      'xMax' => $domain_max,
       'yMin' => $y_min,
       'yMax' => $y_max,
     );
@@ -117,4 +116,49 @@
 
   }
 
+  private function getDomain(array $functions) {
+    $domain_min_list = null;
+    $domain_max_list = null;
+    foreach ($functions as $function) {
+      if ($function->hasDomain()) {
+        $domain = $function->getDomain();
+
+        list($domain_min, $domain_max) = $domain;
+
+        if ($domain_min !== null) {
+          $domain_min_list[] = $domain_min;
+        }
+
+        if ($domain_max !== null) {
+          $domain_max_list[] = $domain_max;
+        }
+      }
+    }
+
+    $domain_min = null;
+    $domain_max = null;
+
+    if ($domain_min_list) {
+      $domain_min = min($domain_min_list);
+    }
+
+    if ($domain_max_list) {
+      $domain_max = max($domain_max_list);
+    }
+
+    // If we don't have any domain data from the actual functions, pick a
+    // plausible domain automatically.
+
+    if ($domain_max === null) {
+      $domain_max = PhabricatorTime::getNow();
+    }
+
+    if ($domain_min === null) {
+      $domain_min = $domain_max - phutil_units('365 days in seconds');
+    }
+
+    return array($domain_min, $domain_max);
+  }
+
+
 }