diff --git a/pageserver/src/consumption_metrics/metrics.rs b/pageserver/src/consumption_metrics/metrics.rs
index 08ab69f349..1627044d64 100644
--- a/pageserver/src/consumption_metrics/metrics.rs
+++ b/pageserver/src/consumption_metrics/metrics.rs
@@ -27,6 +27,9 @@ pub(super) enum Name {
     /// Timeline logical size
     #[serde(rename = "timeline_logical_size")]
     LogicalSize,
+    /// Timeline delta from parent (WAL bytes clamped to logical size)
+    #[serde(rename = "timeline_changed_bytes_from_parent")]
+    ChangedBytesFromParent,
     /// Tenant remote size
     #[serde(rename = "remote_storage_size")]
     RemoteSize,
@@ -175,6 +178,24 @@ impl MetricsKey {
         .absolute_values()
     }
 
+    /// [`Timeline::get_current_lsn`] - [`Timeline::get_ancestor_lsn`], clamped to
+    /// [`Timeline::get_current_logical_size`].
+    ///
+    /// [`Timeline::get_current_lsn`]: crate::tenant::Timeline::get_current_lsn
+    /// [`Timeline::get_ancestor_lsn`]: crate::tenant::Timeline::get_ancestor_lsn
+    /// [`Timeline::get_current_logical_size`]: crate::tenant::Timeline::get_current_logical_size
+    const fn timeline_changed_bytes_from_parent(
+        tenant_id: TenantId,
+        timeline_id: TimelineId,
+    ) -> AbsoluteValueFactory {
+        MetricsKey {
+            tenant_id,
+            timeline_id: Some(timeline_id),
+            metric: Name::ChangedBytesFromParent,
+        }
+        .absolute_values()
+    }
+
     /// [`TenantShard::remote_size`]
     ///
     /// [`TenantShard::remote_size`]: crate::tenant::TenantShard::remote_size
@@ -371,6 +392,7 @@ struct TimelineSnapshot {
     loaded_at: (Lsn, SystemTime),
     last_record_lsn: Lsn,
     current_exact_logical_size: Option<u64>,
+    changed_bytes_from_parent: Option<u64>,
 }
 
 impl TimelineSnapshot {
@@ -406,10 +428,22 @@ impl TimelineSnapshot {
                 }
             };
 
+            // This is an approximation of how much data has changed on this branch vs. its
+            // ancestor: the number of bytes written to the WAL, clamped to the size of the branch.
+            let changed_bytes_from_parent = current_exact_logical_size.and_then(|size| {
+                if t.get_ancestor_lsn() == Lsn::MAX {
+                    return None;
+                }
+                t.get_last_record_lsn()
+                    .checked_sub(t.get_ancestor_lsn())
+                    .map(|wal_bytes| wal_bytes.0.min(size))
+            });
+
             Ok(Some(TimelineSnapshot {
                 loaded_at,
                 last_record_lsn,
                 current_exact_logical_size,
+                changed_bytes_from_parent,
             }))
         }
     }
@@ -487,6 +521,17 @@ impl TimelineSnapshot {
                 metrics.push(factory.at(now, size));
             }
         }
+
+        {
+            let factory = MetricsKey::timeline_changed_bytes_from_parent(tenant_id, timeline_id);
+            let current_or_previous = self
+                .changed_bytes_from_parent
+                .or_else(|| cache.get(factory.key()).map(|item| item.value));
+
+            if let Some(size) = current_or_previous {
+                metrics.push(factory.at(now, size));
+            }
+        }
     }
 }
 
diff --git a/pageserver/src/consumption_metrics/metrics/tests.rs b/pageserver/src/consumption_metrics/metrics/tests.rs
index 52b4fb8680..ea5f8648f4 100644
--- a/pageserver/src/consumption_metrics/metrics/tests.rs
+++ b/pageserver/src/consumption_metrics/metrics/tests.rs
@@ -18,6 +18,7 @@ fn startup_collected_timeline_metrics_before_advancing() {
         loaded_at: (disk_consistent_lsn, SystemTime::now()),
         last_record_lsn: disk_consistent_lsn,
         current_exact_logical_size: Some(0x42000),
+        changed_bytes_from_parent: Some(0x1000),
     };
 
     let now = DateTime::<Utc>::from(SystemTime::now());
@@ -33,7 +34,8 @@ fn startup_collected_timeline_metrics_before_advancing() {
                 0
             ),
             MetricsKey::written_size(tenant_id, timeline_id).at(now, disk_consistent_lsn.0),
-            MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000)
+            MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000),
+            MetricsKey::timeline_changed_bytes_from_parent(tenant_id, timeline_id).at(now, 0x1000)
         ]
     );
 }
@@ -60,6 +62,7 @@ fn startup_collected_timeline_metrics_second_round() {
         loaded_at: (disk_consistent_lsn, init),
         last_record_lsn: disk_consistent_lsn,
         current_exact_logical_size: Some(0x42000),
+        changed_bytes_from_parent: Some(0x1000),
     };
 
     snap.to_metrics(tenant_id, timeline_id, now, &mut metrics, &cache);
@@ -69,7 +72,8 @@ fn startup_collected_timeline_metrics_second_round() {
         &[
             MetricsKey::written_size_delta(tenant_id, timeline_id).from_until(before, now, 0),
             MetricsKey::written_size(tenant_id, timeline_id).at(now, disk_consistent_lsn.0),
-            MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000)
+            MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000),
+            MetricsKey::timeline_changed_bytes_from_parent(tenant_id, timeline_id).at(now, 0x1000)
         ]
     );
 }
@@ -104,6 +108,7 @@ fn startup_collected_timeline_metrics_nth_round_at_same_lsn() {
         loaded_at: (disk_consistent_lsn, init),
         last_record_lsn: disk_consistent_lsn,
         current_exact_logical_size: Some(0x42000),
+        changed_bytes_from_parent: Some(0x1000),
     };
 
     snap.to_metrics(tenant_id, timeline_id, now, &mut metrics, &cache);
@@ -113,7 +118,8 @@ fn startup_collected_timeline_metrics_nth_round_at_same_lsn() {
         &[
             MetricsKey::written_size_delta(tenant_id, timeline_id).from_until(just_before, now, 0),
             MetricsKey::written_size(tenant_id, timeline_id).at(now, disk_consistent_lsn.0),
-            MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000)
+            MetricsKey::timeline_logical_size(tenant_id, timeline_id).at(now, 0x42000),
+            MetricsKey::timeline_changed_bytes_from_parent(tenant_id, timeline_id).at(now, 0x1000)
         ]
     );
 }
@@ -141,6 +147,7 @@ fn post_restart_written_sizes_with_rolled_back_last_record_lsn() {
         loaded_at: (Lsn(50), at_restart),
         last_record_lsn: Lsn(50),
         current_exact_logical_size: None,
+        changed_bytes_from_parent: None,
     };
 
     let mut cache = HashMap::from([
@@ -202,6 +209,7 @@ fn post_restart_current_exact_logical_size_uses_cached() {
         loaded_at: (Lsn(50), at_restart),
         last_record_lsn: Lsn(50),
         current_exact_logical_size: None,
+        changed_bytes_from_parent: Some(0x1000),
     };
 
     let cache = HashMap::from([MetricsKey::timeline_logical_size(tenant_id, timeline_id)
diff --git a/test_runner/regress/test_pageserver_metric_collection.py b/test_runner/regress/test_pageserver_metric_collection.py
index acec0ba44a..cc3fa73890 100644
--- a/test_runner/regress/test_pageserver_metric_collection.py
+++ b/test_runner/regress/test_pageserver_metric_collection.py
@@ -511,4 +511,5 @@ PER_METRIC_VERIFIERS = {
     "written_data_bytes_delta": WrittenDataDeltaVerifier,
     "timeline_logical_size": CannotVerifyAnything,
     "synthetic_storage_size": SyntheticSizeVerifier,
+    "timeline_changed_bytes_from_parent": CannotVerifyAnything,
 }