diff --git a/_python_utils_tests/test_formatters.py b/_python_utils_tests/test_formatters.py
index e683c88..ad38c36 100644
--- a/_python_utils_tests/test_formatters.py
+++ b/_python_utils_tests/test_formatters.py
@@ -1,7 +1,9 @@
 """Tests for the formatting helpers in ``python_utils.formatters``."""
 
 import datetime
+import types
 import typing
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
 
 import pytest
 
@@ -55,6 +57,107 @@ def test_timesince_aware_datetime(timezone: datetime.timezone) -> None:
     assert formatters.timesince(moment) == '1 hour and 30 minutes ago'
 
 
+@pytest.mark.parametrize(
+    ('moment', 'current'),
+    [
+        (
+            datetime.datetime(2026, 11, 1, 1, 30, fold=0),
+            datetime.datetime(2026, 11, 1, 1, 30, fold=1),
+        ),
+        (
+            datetime.datetime(2026, 11, 1, 1, 30, fold=1),
+            datetime.datetime(2026, 11, 1, 1, 30, fold=0),
+        ),
+        (
+            datetime.datetime(2026, 3, 8, 1, 30),
+            datetime.datetime(2026, 3, 8, 3, 30),
+        ),
+        (
+            datetime.datetime(2026, 3, 8, 3, 30),
+            datetime.datetime(2026, 3, 8, 1, 30),
+        ),
+    ],
+    ids=['fall-back-past', 'fall-back-future', 'spring-past', 'spring-future'],
+)
+def test_timesince_counts_elapsed_time_across_dst(
+    moment: datetime.datetime,
+    current: datetime.datetime,
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Count elapsed time when both datetimes share a changing UTC offset."""
+    try:
+        timezone = ZoneInfo('America/New_York')
+    except ZoneInfoNotFoundError:
+        pytest.skip('IANA timezone data is not available')
+    current = current.replace(tzinfo=timezone)
+    moment = moment.replace(tzinfo=timezone)
+
+    class FrozenDateTime(datetime.datetime):
+        """Return the chosen instant as the current time."""
+
+        @classmethod
+        def now(cls, tz: datetime.tzinfo | None = None) -> 'FrozenDateTime':
+            """Keep the same instant while returning the requested timezone."""
+            return cls.fromtimestamp(current.timestamp(), tz)
+
+    monkeypatch.setattr(
+        formatters,
+        'datetime',
+        types.SimpleNamespace(
+            datetime=FrozenDateTime,
+            timedelta=datetime.timedelta,
+            timezone=datetime.timezone,
+        ),
+    )
+    assert formatters.timesince(moment) == '1 hour ago'
+
+
+@pytest.mark.parametrize(
+    ('moment', 'expected'),
+    [
+        (
+            datetime.datetime.min.replace(
+                tzinfo=datetime.timezone(datetime.timedelta(hours=1))
+            ),
+            '2000 years and 3 months ago',
+        ),
+        (
+            datetime.datetime.max.replace(
+                tzinfo=datetime.timezone(datetime.timedelta(hours=-1))
+            ),
+            '8005 years and 3 months ago',
+        ),
+    ],
+    ids=['min-positive-offset', 'max-negative-offset'],
+)
+def test_timesince_aware_datetime_boundaries(
+    moment: datetime.datetime,
+    expected: str,
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Accept aware inputs whose corresponding UTC date is out of range."""
+    current = datetime.datetime(2000, 1, 1, tzinfo=datetime.timezone.utc)
+
+    class FrozenDateTime(datetime.datetime):
+        """Return the chosen instant as the current time."""
+
+        @classmethod
+        def now(cls, tz: datetime.tzinfo | None = None) -> 'FrozenDateTime':
+            """Keep the same instant while returning the requested timezone."""
+            return cls.fromtimestamp(current.timestamp(), tz)
+
+    monkeypatch.setattr(
+        formatters,
+        'datetime',
+        types.SimpleNamespace(
+            datetime=FrozenDateTime,
+            timedelta=datetime.timedelta,
+            timezone=datetime.timezone,
+        ),
+    )
+    assert formatters.timesince(moment) == expected
+
+
 @pytest.mark.parametrize(
     ('name', 'expected'),
     [
diff --git a/docs/guide/conversions-and-formatting.md b/docs/guide/conversions-and-formatting.md
index 11b1d6a..14d3c41 100644
--- a/docs/guide/conversions-and-formatting.md
+++ b/docs/guide/conversions-and-formatting.md
@@ -96,4 +96,7 @@ time.format_time(datetime.datetime(2000, 1, 2, 3, 4, 5))     # '2000-01-02 03:04
 time.format_time(None)                                       # '--:--:--'
 ```
 
+For timezone-aware datetimes, `timesince` counts elapsed time across daylight
+saving transitions. Naive datetimes are compared with the current local time.
+
 See the {doc}`API reference <../python_utils>` for every parameter.
diff --git a/python_utils/formatters.py b/python_utils/formatters.py
index 71082c4..18601ef 100644
--- a/python_utils/formatters.py
+++ b/python_utils/formatters.py
@@ -150,6 +150,13 @@ def timesince(
         # A date has no `tzinfo`, and no time to subtract either. It gets
         # the same `TypeError` from the subtraction as it always did.
         now = datetime.datetime.now(getattr(dt, 'tzinfo', None))
+        if (
+            getattr(dt, 'tzinfo', None) is not None
+            and dt.utcoffset() is not None
+        ):
+            # Subtraction with the same tzinfo ignores offset changes and fold.
+            # Convert only now: converting dt could overflow near min or max.
+            now = now.astimezone(datetime.timezone.utc)
         diff = abs(now - dt)
 
     # Every unit takes its share from what the larger units left over, so a