BUG: Timestamp origin takes no effect in resample for 'MS' frequency

doc/source/whatsnew/v2.1.0.rst

@@ -475,6 +475,7 @@ Plotting
 
 Groupby/resample/rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^
+- Bug in :meth:`DataFrame.resample` and :meth:`Series.resample` :class:`Datetimelike` ``origin`` has no effect in resample for ``MS`` frequency (:issue:`53662`)
 - Bug in :meth:`DataFrame.resample` and :meth:`Series.resample` in incorrectly allowing non-fixed ``freq`` when resampling on a :class:`TimedeltaIndex` (:issue:`51896`)
 - Bug in :meth:`DataFrame.resample` and :meth:`Series.resample` losing time zone when resampling empty data (:issue:`53664`)
 - Bug in :meth:`DataFrameGroupBy.idxmin`, :meth:`SeriesGroupBy.idxmin`, :meth:`DataFrameGroupBy.idxmax`, :meth:`SeriesGroupBy.idxmax` return wrong dtype when used on empty DataFrameGroupBy or SeriesGroupBy (:issue:`51423`)

pandas/core/resample.py

@@ -2330,7 +2330,13 @@ def _get_timestamp_range_edges(
         last = last.normalize()
 
         if closed == "left":
-            first = Timestamp(freq.rollback(first))
+            if isinstance(origin, Timestamp):
+                if first - freq >= origin:
+                    first = Timestamp(first - freq)
+                else:
+                    first = Timestamp(freq.rollback(first))
+            else:
+                first = Timestamp(freq.rollback(first))
         else:
             first = Timestamp(first - freq)
 

pandas/tests/resample/test_datetime_index.py

@@ -838,6 +838,23 @@ def test_resample_bad_offset(offset, unit):
         ts.resample("5min", offset=offset)
 
 
+def test_resample_monthstart_origin():
+    # GH 53662
+    df = DataFrame({"ts": [datetime(1999, 12, 31, 0, 0, 0)], "values": [10.0]})
+
+    result = df.resample("2MS", on="ts", origin="1999-11-01", closed="right")[
+        "values"
+    ].sum()
+    excepted = Series(
+        [10.0],
+        index=DatetimeIndex(
+            ["1999-11-01"], dtype="datetime64[ns]", name="ts", freq="2MS"
+        ),
+    )
+
+    tm.assert_index_equal(result.index, excepted.index)
+
+
 def test_resample_origin_prime_freq(unit):
     # GH 31809
     start, end = "2000-10-01 23:30:00", "2000-10-02 00:30:00"