diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/EventTimeWatermark.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/EventTimeWatermark.scala
index 8441c2c481ec..2309aa42b80c 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/EventTimeWatermark.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/EventTimeWatermark.scala
@@ -17,9 +17,8 @@
 
 package org.apache.spark.sql.catalyst.plans.logical
 
-import java.util.concurrent.TimeUnit
-
 import org.apache.spark.sql.catalyst.expressions.Attribute
+import org.apache.spark.sql.catalyst.util.DateTimeUtils.MILLIS_PER_MONTH
 import org.apache.spark.sql.types.MetadataBuilder
 import org.apache.spark.unsafe.types.CalendarInterval
 
@@ -28,9 +27,7 @@ object EventTimeWatermark {
   val delayKey = "spark.watermarkDelayMs"
 
   def getDelayMs(delay: CalendarInterval): Long = {
-    // We define month as `31 days` to simplify calculation.
-    val millisPerMonth = TimeUnit.MICROSECONDS.toMillis(CalendarInterval.MICROS_PER_DAY) * 31
-    delay.milliseconds + delay.months * millisPerMonth
+    delay.milliseconds + delay.months * MILLIS_PER_MONTH
   }
 }
 
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala
index 34e8012106bb..79fc45ec8947 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala
@@ -59,6 +59,15 @@ object DateTimeUtils {
   final val MILLIS_PER_MINUTE: Long = 60 * MILLIS_PER_SECOND
   final val MILLIS_PER_HOUR: Long = 60 * MILLIS_PER_MINUTE
   final val MILLIS_PER_DAY: Long = SECONDS_PER_DAY * MILLIS_PER_SECOND
+  // The average year of the Gregorian calendar 365.2425 days long, see
+  // https://en.wikipedia.org/wiki/Gregorian_calendar
+  // Leap year occurs every 4 years, except for years that are divisible by 100
+  // and not divisible by 400. So, the mean length of of the Gregorian calendar year is:
+  //  1 mean year = (365 + 1/4 - 1/100 + 1/400) days = 365.2425 days
+  // The mean year length in seconds is:
+  //  60 * 60 * 24 * 365.2425 = 31556952.0 = 12 * 2629746
+  final val SECONDS_PER_MONTH: Int = 2629746
+  final val MILLIS_PER_MONTH: Long = SECONDS_PER_MONTH * MILLIS_PER_SECOND
 
   // number of days between 1.1.1970 and 1.1.2001
   final val to2001 = -11323
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/GroupStateImpl.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/GroupStateImpl.scala
index dda9d41f630e..f459a2c1f8e2 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/GroupStateImpl.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/GroupStateImpl.scala
@@ -18,9 +18,9 @@
 package org.apache.spark.sql.execution.streaming
 
 import java.sql.Date
-import java.util.concurrent.TimeUnit
 
 import org.apache.spark.sql.catalyst.plans.logical.{EventTimeTimeout, ProcessingTimeTimeout}
+import org.apache.spark.sql.catalyst.util.DateTimeUtils.MILLIS_PER_MONTH
 import org.apache.spark.sql.execution.streaming.GroupStateImpl._
 import org.apache.spark.sql.streaming.{GroupState, GroupStateTimeout}
 import org.apache.spark.unsafe.types.CalendarInterval
@@ -164,8 +164,7 @@ private[sql] class GroupStateImpl[S] private(
       throw new IllegalArgumentException(s"Provided duration ($duration) is not positive")
     }
 
-    val millisPerMonth = TimeUnit.MICROSECONDS.toMillis(CalendarInterval.MICROS_PER_DAY) * 31
-    cal.milliseconds + cal.months * millisPerMonth
+    cal.milliseconds + cal.months * MILLIS_PER_MONTH
   }
 
   private def checkTimeoutTimestampAllowed(): Unit = {