diff --git a/litellm/proxy/spend_tracking/spend_management_endpoints.py b/litellm/proxy/spend_tracking/spend_management_endpoints.py
index 84278f4619d..67e10b37e3c 100644
--- a/litellm/proxy/spend_tracking/spend_management_endpoints.py
+++ b/litellm/proxy/spend_tracking/spend_management_endpoints.py
@@ -324,7 +324,7 @@ SELECT
     model,
     SUM(spend) AS spend
 FROM "LiteLLM_SpendLogs"
-WHERE "startTime" >= ($1::timestamptz AT TIME ZONE 'UTC') AND "startTime" <= ($2::timestamptz AT TIME ZONE 'UTC')
+WHERE "startTime" >= ($1::timestamptz AT TIME ZONE 'UTC') AND "startTime" < ($2::timestamptz AT TIME ZONE 'UTC')
 {filter_sql}
 GROUP BY 1, 2, 3, 4
 ORDER BY 1
@@ -3584,14 +3584,14 @@ async def view_spend_logs(
             start_date_obj: Final = datetime.strptime(start_date, "%Y-%m-%d").replace(tzinfo=timezone.utc)
             end_date_obj: Final = datetime.strptime(end_date, "%Y-%m-%d").replace(tzinfo=timezone.utc)
 
-            # Convert to ISO format strings for Prisma
+            # end_date is a calendar day, so the window ends at the next midnight (exclusive)
             start_date_iso: Final = start_date_obj.isoformat()
-            end_date_iso: Final = end_date_obj.isoformat()
+            end_date_iso: Final = (end_date_obj + timedelta(days=1)).isoformat()
 
             filter_query: Final[dict[str, object]] = {
                 "startTime": {
                     "gte": start_date_iso,  # Greater than or equal to Start Date
-                    "lte": end_date_iso,  # Less than or equal to End Date
+                    "lt": end_date_iso,  # Before the day after End Date
                 }
             }
 
diff --git a/tests/unit/proxy/spend_tracking/test_spend_logs_date_window.py b/tests/unit/proxy/spend_tracking/test_spend_logs_date_window.py
new file mode 100644
index 00000000000..9eea52ead78
--- /dev/null
+++ b/tests/unit/proxy/spend_tracking/test_spend_logs_date_window.py
@@ -0,0 +1,81 @@
+"""/spend/logs treats end_date as a whole calendar day (#40216)."""
+
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+from fastapi import Response
+
+import litellm.proxy.spend_tracking.spend_management_endpoints as spend_endpoints
+from litellm.proxy import proxy_server
+from litellm.proxy._types import LitellmUserRoles, UserAPIKeyAuth
+from litellm.proxy.spend_tracking.spend_management_endpoints import (
+    _spend_logs_daily_summary_sql,
+    view_spend_logs,
+)
+
+
+def _admin() -> UserAPIKeyAuth:
+    return UserAPIKeyAuth(user_role=LitellmUserRoles.PROXY_ADMIN, api_key="sk-admin")
+
+
+def test_daily_summary_sql_uses_exclusive_upper_bound():
+    sql, _ = _spend_logs_daily_summary_sql(
+        start_date_iso="2026-09-07T00:00:00+00:00",
+        end_date_iso="2026-09-08T00:00:00+00:00",
+        api_key=None,
+        request_id=None,
+        user_id=None,
+    )
+    assert "\"startTime\" < ($2::timestamptz AT TIME ZONE 'UTC')" in sql
+    assert "<= ($2" not in sql
+
+
+@pytest.mark.asyncio
+async def test_summary_queries_through_end_of_end_date(monkeypatch):
+    prisma = MagicMock()
+    prisma.db.query_raw = AsyncMock(
+        return_value=[{"day": "2026-09-08", "api_key": "k", "user": "u", "model": "m", "spend": 1.5}]
+    )
+    monkeypatch.setattr(proxy_server, "prisma_client", prisma)
+
+    result = await view_spend_logs(
+        fastapi_response=Response(),
+        api_key=None,
+        user_id=None,
+        request_id=None,
+        start_date="2026-09-08",
+        end_date="2026-09-08",
+        summarize=True,
+        user_api_key_dict=_admin(),
+    )
+
+    params = prisma.db.query_raw.call_args[0][1:]
+    assert params[0] == "2026-09-08T00:00:00+00:00"
+    assert params[1] == "2026-09-09T00:00:00+00:00"
+    # The real end-day row is returned and no synthetic zero row is appended.
+    assert len(result) == 1
+    assert result[0]["spend"] == 1.5
+
+
+@pytest.mark.asyncio
+async def test_unsummarized_filter_includes_end_date(monkeypatch):
+    find_spend_logs = AsyncMock(return_value=[])
+    monkeypatch.setattr(proxy_server, "prisma_client", MagicMock())
+    monkeypatch.setattr(spend_endpoints, "_find_spend_logs", find_spend_logs)
+
+    await view_spend_logs(
+        fastapi_response=Response(),
+        api_key=None,
+        user_id=None,
+        request_id=None,
+        start_date="2026-09-07",
+        end_date="2026-09-07",
+        summarize=False,
+        user_api_key_dict=_admin(),
+    )
+
+    where = find_spend_logs.call_args.kwargs["where"]
+    assert where["startTime"] == {
+        "gte": "2026-09-07T00:00:00+00:00",
+        "lt": "2026-09-08T00:00:00+00:00",
+    }
diff --git a/tests/unit/proxy/spend_tracking/test_spend_management_endpoints.py b/tests/unit/proxy/spend_tracking/test_spend_management_endpoints.py
index 23bbe521670..2bdde01a7b9 100644
--- a/tests/unit/proxy/spend_tracking/test_spend_management_endpoints.py
+++ b/tests/unit/proxy/spend_tracking/test_spend_management_endpoints.py
@@ -4497,7 +4497,7 @@ async def test_view_spend_logs_summarize_groups_by_day_in_sql(client, monkeypatc
         assert not hasattr(mock_prisma_client.db, "group_by")
         assert mock_prisma_client.db.captured_params == (
             "2024-01-01T00:00:00+00:00",
-            "2024-01-03T00:00:00+00:00",
+            "2024-01-04T00:00:00+00:00",
             "hashed::sk-abc",
             "req-123",
             "u1",
@@ -4591,7 +4591,7 @@ async def test_view_spend_logs_summarize_unhashed_api_key_without_padding(client
         data = response.json()
         assert mock_prisma_client.db.captured_params == (
             "2024-01-01T00:00:00+00:00",
-            "2024-01-01T00:00:00+00:00",
+            "2024-01-02T00:00:00+00:00",
             "plain-key",
         )
         assert data == [