diff --git a/litellm/litellm_core_utils/llm_cost_calc/utils.py b/litellm/litellm_core_utils/llm_cost_calc/utils.py
index be289f620cf..30c25253eea 100644
--- a/litellm/litellm_core_utils/llm_cost_calc/utils.py
+++ b/litellm/litellm_core_utils/llm_cost_calc/utils.py
@@ -296,7 +296,8 @@ def _is_within_off_peak_window(off_peak_hours_utc: str | Sequence[str], current_
 
     off_peak_hours_utc is a "HH:MM-HH:MM" string in UTC, or a list of such strings for providers
     with multiple daily windows (e.g. ["16:30-00:30", "04:00-06:00"]). A window may wrap past
-    midnight. The start is inclusive and the end is exclusive; malformed windows are ignored.
+    midnight, and a window whose start equals its end covers the whole day. The start is
+    inclusive and the end is exclusive; malformed windows are ignored.
     """
     reference: Final = current_time if current_time is not None else datetime.now(timezone.utc)
     now: Final = (reference.astimezone(timezone.utc) if reference.tzinfo is not None else reference).time()
@@ -308,7 +309,7 @@ def _is_within_off_peak_window(off_peak_hours_utc: str | Sequence[str], current_
             end = datetime.strptime(end_str.strip(), "%H:%M").replace(tzinfo=timezone.utc).time()
         except (ValueError, AttributeError):
             continue
-        if start <= end:
+        if start < end:
             if start <= now < end:
                 return True
         elif now >= start or now < end:
diff --git a/tests/test_litellm/litellm_core_utils/llm_cost_calc/test_llm_cost_calc_utils.py b/tests/test_litellm/litellm_core_utils/llm_cost_calc/test_llm_cost_calc_utils.py
index 8f348b36d35..c9ed5936f03 100644
--- a/tests/test_litellm/litellm_core_utils/llm_cost_calc/test_llm_cost_calc_utils.py
+++ b/tests/test_litellm/litellm_core_utils/llm_cost_calc/test_llm_cost_calc_utils.py
@@ -431,6 +431,19 @@ def test_is_within_off_peak_window_wraps_midnight():
     assert _is_within_off_peak_window(window, datetime(2026, 1, 1, 12, 0, tzinfo=timezone.utc)) is False
 
 
+def test_is_within_off_peak_window_equal_start_and_end_covers_whole_day():
+    """An equal start and end is the natural way to spell off-peak all day. It used to take the
+    non-wrap branch, where start <= now < end can never hold, so it matched nothing and billed at
+    standard rates around the clock without raising or logging anything."""
+    from datetime import datetime, timezone
+
+    for window in ("00:00-00:00", "10:00-10:00"):
+        for hour in range(24):
+            assert (
+                _is_within_off_peak_window(window, datetime(2026, 1, 1, hour, 0, tzinfo=timezone.utc)) is True
+            ), f"{window} should cover {hour:02d}:00"
+
+
 def test_is_within_off_peak_window_multiple_windows():
     from datetime import datetime, timezone