diff --git a/src/backend/core/migrations/0026_item_item_creator_size_not_hdel_idx.py b/src/backend/core/migrations/0026_item_item_creator_size_not_hdel_idx.py
new file mode 100644
index 00000000..da815757
--- /dev/null
+++ b/src/backend/core/migrations/0026_item_item_creator_size_not_hdel_idx.py
@@ -0,0 +1,22 @@
+# Generated by Django 5.2.14 on 2026-07-08 10:14
+
+from django.contrib.postgres.operations import AddIndexConcurrently
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    # CREATE INDEX CONCURRENTLY cannot run inside a transaction. It avoids
+    # locking writes on the item table while the index is being built.
+    atomic = False
+
+    dependencies = [
+        ('core', '0025_user_storage_limit_override'),
+    ]
+
+    operations = [
+        AddIndexConcurrently(
+            model_name='item',
+            index=models.Index(condition=models.Q(('hard_deleted_at__isnull', True)), fields=['creator'], include=('size',), name='item_creator_size_not_hdel_idx'),
+        ),
+    ]
diff --git a/src/backend/core/models.py b/src/backend/core/models.py
index 2c8df87b..d91bfce4 100644
--- a/src/backend/core/models.py
+++ b/src/backend/core/models.py
@@ -1034,6 +1034,13 @@ class Item(TreeModel, BaseModel):
         indexes = [
             GistIndex(fields=["path"]),
             models.Index(NLevel(models.F("path")), name="drive_item_path_nlevel_idx"),
+            # Covers the storage used computation by creator.
+            models.Index(
+                fields=["creator"],
+                include=["size"],
+                condition=models.Q(hard_deleted_at__isnull=True),
+                name="item_creator_size_not_hdel_idx",
+            ),
         ]
 
     def __str__(self):
diff --git a/src/backend/core/storage/creator_storage_compute_backend.py b/src/backend/core/storage/creator_storage_compute_backend.py
index a21864c2..c2fb7082 100644
--- a/src/backend/core/storage/creator_storage_compute_backend.py
+++ b/src/backend/core/storage/creator_storage_compute_backend.py
@@ -15,6 +15,6 @@ class CreatorStorageComputeBackend(StorageComputeBackend):
         """
         Compute the total storage used by a set of users.
         """
-        return Item.objects.filter(creator__in=users).aggregate(total_size=Sum("size", default=0))[
-            "total_size"
-        ]
+        return Item.objects.filter(creator__in=users, hard_deleted_at__isnull=True).aggregate(
+            total_size=Sum("size", default=0)
+        )["total_size"]
diff --git a/src/backend/core/tests/storage/test_creator_storage_compute_backend.py b/src/backend/core/tests/storage/test_creator_storage_compute_backend.py
new file mode 100644
index 00000000..21d9b6f0
--- /dev/null
+++ b/src/backend/core/tests/storage/test_creator_storage_compute_backend.py
@@ -0,0 +1,41 @@
+"""
+Tests for the CreatorStorageComputeBackend.
+"""
+
+import pytest
+
+from core import factories
+from core.storage.creator_storage_compute_backend import CreatorStorageComputeBackend
+
+pytestmark = pytest.mark.django_db
+
+
+def test_compute_storage_used_sums_creator_items():
+    """The backend should sum the sizes of all items created by the given users."""
+    user = factories.UserFactory()
+    factories.ItemFactory(creator=user, size=100)
+    factories.ItemFactory(creator=user, size=250)
+    factories.ItemFactory(size=999)  # another creator, should not count
+
+    assert CreatorStorageComputeBackend().compute_storage_used([user]) == 350
+
+
+def test_compute_storage_used_excludes_hard_deleted_items():
+    """Hard-deleted items should not count toward the storage used."""
+    user = factories.UserFactory()
+    factories.ItemFactory(creator=user, size=100)
+    hard_deleted = factories.ItemFactory(creator=user, size=250)
+    hard_deleted.soft_delete()
+    hard_deleted.hard_delete()
+
+    assert CreatorStorageComputeBackend().compute_storage_used([user]) == 100
+
+
+def test_compute_storage_used_keeps_soft_deleted_items():
+    """Soft-deleted (trashbin) items should still count toward the storage used."""
+    user = factories.UserFactory()
+    factories.ItemFactory(creator=user, size=100)
+    soft_deleted = factories.ItemFactory(creator=user, size=250)
+    soft_deleted.soft_delete()
+
+    assert CreatorStorageComputeBackend().compute_storage_used([user]) == 350