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
@@ -568,6 +568,7 @@
     'phutil_json_encode' => 'utils/utils.php',
     'phutil_load_library' => 'moduleutils/core.php',
     'phutil_loggable_string' => 'utils/utils.php',
+    'phutil_microseconds_since' => 'utils/utils.php',
     'phutil_parse_bytes' => 'utils/viewutils.php',
     'phutil_passthru' => 'future/exec/execx.php',
     'phutil_person' => 'internationalization/pht.php',
diff --git a/src/utils/utils.php b/src/utils/utils.php
--- a/src/utils/utils.php
+++ b/src/utils/utils.php
@@ -1137,6 +1137,29 @@
 }
 
 
+/**
+ * Compute the number of microseconds that have elapsed since an earlier
+ * timestamp (from `microtime(true)`).
+ *
+ * @param double Microsecond-precision timestamp, from `microtime(true)`.
+ * @return int Elapsed microseconds.
+ */
+function phutil_microseconds_since($timestamp) {
+  if (!is_float($timestamp)) {
+    throw new Exception(
+      pht(
+        'Argument to "phutil_microseconds_since(...)" should be a value '.
+        'returned from "microtime(true)".'));
+  }
+
+  $delta = (microtime(true) - $timestamp);
+  $delta = 1000000 * $delta;
+  $delta = (int)$delta;
+
+  return $delta;
+}
+
+
 /**
  * Decode a JSON dictionary.
  *