diff --git a/sdks/go/pkg/beam/transforms/periodic/periodic.go b/sdks/go/pkg/beam/transforms/periodic/periodic.go
index 84ee50f2ae6c..cc9c342b9125 100644
--- a/sdks/go/pkg/beam/transforms/periodic/periodic.go
+++ b/sdks/go/pkg/beam/transforms/periodic/periodic.go
@@ -61,8 +61,8 @@ func NewSequenceDefinition(start, end time.Time, interval time.Duration) Sequenc
 	}
 }
 
-func CalculateByteSizeOfSequence(now time.Time, sd SequenceDefinition, rest offsetrange.Restriction) int64 {
-	// Find the # of outputs expected for overlap of  and [-inf, now)
+// Calculates size of the output that the sequence should have emitted up to now.
+func calculateSequenceByteSize(now time.Time, sd SequenceDefinition, rest offsetrange.Restriction) int64 {
 	nowIndex := int64(now.Sub(mtime.Time(sd.Start).ToTime()) / sd.Interval)
 	if nowIndex < rest.Start {
 		return 0
@@ -85,7 +85,7 @@ func (fn *sequenceGenDoFn) CreateTracker(rest offsetrange.Restriction) *sdf.Lock
 }
 
 func (fn *sequenceGenDoFn) RestrictionSize(sd SequenceDefinition, rest offsetrange.Restriction) float64 {
-	return float64(CalculateByteSizeOfSequence(time.Now(), sd, rest))
+	return float64(calculateSequenceByteSize(time.Now(), sd, rest))
 }
 
 func (fn *sequenceGenDoFn) SplitRestriction(_ SequenceDefinition, rest offsetrange.Restriction) []offsetrange.Restriction {
diff --git a/sdks/go/pkg/beam/transforms/periodic/periodic_test.go b/sdks/go/pkg/beam/transforms/periodic/periodic_test.go
index 56dba8778684..26f94be5b4e9 100644
--- a/sdks/go/pkg/beam/transforms/periodic/periodic_test.go
+++ b/sdks/go/pkg/beam/transforms/periodic/periodic_test.go
@@ -79,7 +79,7 @@ func TestSize(t *testing.T) {
 	}
 
 	for _, test := range sizeTests {
-		got := CalculateByteSizeOfSequence(
+		got := calculateSequenceByteSize(
 			time.Unix(test.now, 0),
 			sd,
 			offsetrange.Restriction{
diff --git a/sdks/python/apache_beam/transforms/periodicsequence.py b/sdks/python/apache_beam/transforms/periodicsequence.py
index 61c9aacd920c..613661b22957 100644
--- a/sdks/python/apache_beam/transforms/periodicsequence.py
+++ b/sdks/python/apache_beam/transforms/periodicsequence.py
@@ -49,15 +49,17 @@ def create_tracker(self, restriction):
     return OffsetRestrictionTracker(restriction)
 
   def restriction_size(self, element, restriction):
-    return sequence_backlog_bytes(element, time.time(), restriction)
+    return _sequence_backlog_bytes(element, time.time(), restriction)
 
   # On drain, immediately stop emitting new elements
   def truncate(self, unused_element, unused_restriction):
     return None
 
 
-def sequence_backlog_bytes(element, now, offset_range):
-  # Find the # of outputs expected for overlap of  and [-inf, now)
+def _sequence_backlog_bytes(element, now, offset_range):
+  '''
+  Calculates size of the output that the sequence should have emitted up to now.
+  '''
   start, _, interval = element
   if isinstance(start, Timestamp):
     start = start.micros / 1000000
@@ -66,6 +68,8 @@ def sequence_backlog_bytes(element, now, offset_range):
   now_index = math.floor((now - start) / interval)
   if now_index < offset_range.start:
     return 0
+  # We attempt to be precise as some runners scale based upon bytes and
+  # output byte throughput.
   return 8 * (min(offset_range.stop, now_index) - offset_range.start)
 
 
diff --git a/sdks/python/apache_beam/transforms/periodicsequence_test.py b/sdks/python/apache_beam/transforms/periodicsequence_test.py
index 58b3c2a61b87..221520c94622 100644
--- a/sdks/python/apache_beam/transforms/periodicsequence_test.py
+++ b/sdks/python/apache_beam/transforms/periodicsequence_test.py
@@ -30,7 +30,7 @@
 from apache_beam.testing.util import equal_to
 from apache_beam.transforms.periodicsequence import PeriodicImpulse
 from apache_beam.transforms.periodicsequence import PeriodicSequence
-from apache_beam.transforms.periodicsequence import sequence_backlog_bytes
+from apache_beam.transforms.periodicsequence import _sequence_backlog_bytes
 
 # Disable frequent lint warning due to pipe operator for chaining transforms.
 # pylint: disable=expression-not-assigned
@@ -117,20 +117,20 @@ def test_periodicsequence_outputs_valid_sequence_in_past(self):
   def test_periodicsequence_output_size(self):
     element = [0, 1000000000, 10]
     self.assertEqual(
-        sequence_backlog_bytes(element, 100, OffsetRange(10, 100000000)), 0)
+        _sequence_backlog_bytes(element, 100, OffsetRange(10, 100000000)), 0)
     self.assertEqual(
-        sequence_backlog_bytes(element, 100, OffsetRange(9, 100000000)), 8)
+        _sequence_backlog_bytes(element, 100, OffsetRange(9, 100000000)), 8)
     self.assertEqual(
-        sequence_backlog_bytes(element, 100, OffsetRange(8, 100000000)), 16)
+        _sequence_backlog_bytes(element, 100, OffsetRange(8, 100000000)), 16)
     self.assertEqual(
-        sequence_backlog_bytes(element, 101, OffsetRange(9, 100000000)), 8)
+        _sequence_backlog_bytes(element, 101, OffsetRange(9, 100000000)), 8)
     self.assertEqual(
-        sequence_backlog_bytes(element, 10000, OffsetRange(0, 100000000)),
+        _sequence_backlog_bytes(element, 10000, OffsetRange(0, 100000000)),
         8 * 10000 / 10)
     self.assertEqual(
-        sequence_backlog_bytes(element, 10000, OffsetRange(1002, 1003)), 0)
+        _sequence_backlog_bytes(element, 10000, OffsetRange(1002, 1003)), 0)
     self.assertEqual(
-        sequence_backlog_bytes(element, 10100, OffsetRange(1002, 1003)), 8)
+        _sequence_backlog_bytes(element, 10100, OffsetRange(1002, 1003)), 8)
 
 
 if __name__ == '__main__':