diff --git a/shared/timespec-util.h b/shared/timespec-util.h
index 958adb0..576b3e8 100644
--- a/shared/timespec-util.h
+++ b/shared/timespec-util.h
@@ -93,6 +93,20 @@
 	return (int64_t)a->tv_sec * NSEC_PER_SEC + a->tv_nsec;
 }
 
+/* Subtract timespecs and return result in nanoseconds
+ *
+ * \param a[in] operand
+ * \param b[in] operand
+ * \return to_nanoseconds(a - b)
+ */
+static inline int64_t
+timespec_sub_to_nsec(const struct timespec *a, const struct timespec *b)
+{
+	struct timespec r;
+	timespec_sub(&r, a, b);
+	return timespec_to_nsec(&r);
+}
+
 /* Convert timespec to milliseconds
  *
  * \param a timespec
@@ -106,6 +120,18 @@
 	return (int64_t)a->tv_sec * 1000 + a->tv_nsec / 1000000;
 }
 
+/* Subtract timespecs and return result in milliseconds
+ *
+ * \param a[in] operand
+ * \param b[in] operand
+ * \return to_milliseconds(a - b)
+ */
+static inline int64_t
+timespec_sub_to_msec(const struct timespec *a, const struct timespec *b)
+{
+	return timespec_sub_to_nsec(a, b) / 1000000;
+}
+
 /* Convert milli-Hertz to nanoseconds
  *
  * \param mhz frequency in mHz, not zero