diff --git a/narwhals/_pandas_like/utils.py b/narwhals/_pandas_like/utils.py
index 29fc9d4d24..c7661d2a59 100644
--- a/narwhals/_pandas_like/utils.py
+++ b/narwhals/_pandas_like/utils.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import functools
+import operator
 import re
 from typing import TYPE_CHECKING, Any, Callable, Literal, TypeVar
 
@@ -44,6 +45,10 @@
     from narwhals.typing import DTypeBackend, IntoDType, TimeUnit, _1DArray
 
     ExprT = TypeVar("ExprT", bound=PandasLikeExpr)
+    UnitCurrent: TypeAlias = TimeUnit
+    UnitTarget: TypeAlias = TimeUnit
+    BinOpBroadcast: TypeAlias = Callable[[Any, int], Any]
+    IntoRhs: TypeAlias = int
 
 
 PANDAS_LIKE_IMPLEMENTATION = {
@@ -553,52 +558,47 @@ def int_dtype_mapper(dtype: Any) -> str:
     return "int64"
 
 
-def calculate_timestamp_datetime(  # noqa: C901, PLR0912
-    s: NativeSeriesT, original_time_unit: str, time_unit: str
+_TIMESTAMP_DATETIME_OP_FACTOR: Mapping[
+    tuple[UnitCurrent, UnitTarget], tuple[BinOpBroadcast, IntoRhs]
+] = {
+    ("ns", "us"): (operator.floordiv, 1_000),
+    ("ns", "ms"): (operator.floordiv, 1_000_000),
+    ("us", "ns"): (operator.mul, NS_PER_MICROSECOND),
+    ("us", "ms"): (operator.floordiv, 1_000),
+    ("ms", "ns"): (operator.mul, NS_PER_MILLISECOND),
+    ("ms", "us"): (operator.mul, 1_000),
+    ("s", "ns"): (operator.mul, NS_PER_SECOND),
+    ("s", "us"): (operator.mul, US_PER_SECOND),
+    ("s", "ms"): (operator.mul, MS_PER_SECOND),
+}
+
+
+def calculate_timestamp_datetime(
+    s: NativeSeriesT, current: TimeUnit, time_unit: TimeUnit
 ) -> NativeSeriesT:
-    if original_time_unit == "ns":
-        if time_unit == "ns":
-            result = s
-        elif time_unit == "us":
-            result = s // 1_000
-        else:
-            result = s // 1_000_000
-    elif original_time_unit == "us":
-        if time_unit == "ns":
-            result = s * NS_PER_MICROSECOND
-        elif time_unit == "us":
-            result = s
-        else:
-            result = s // 1_000
-    elif original_time_unit == "ms":
-        if time_unit == "ns":
-            result = s * NS_PER_MILLISECOND
-        elif time_unit == "us":
-            result = s * 1_000
-        else:
-            result = s
-    elif original_time_unit == "s":
-        if time_unit == "ns":
-            result = s * NS_PER_SECOND
-        elif time_unit == "us":
-            result = s * US_PER_SECOND
-        else:
-            result = s * MS_PER_SECOND
+    if current == time_unit:
+        return s
+    elif item := _TIMESTAMP_DATETIME_OP_FACTOR.get((current, time_unit)):
+        fn, factor = item
+        return fn(s, factor)
     else:  # pragma: no cover
-        msg = f"unexpected time unit {original_time_unit}, please report a bug at https://github.com/narwhals-dev/narwhals"
+        msg = (
+            f"unexpected time unit {current}, please report an issue at "
+            "https://github.com/narwhals-dev/narwhals"
+        )
         raise AssertionError(msg)
-    return result
-
-
-def calculate_timestamp_date(s: NativeSeriesT, time_unit: str) -> NativeSeriesT:
-    s = s * SECONDS_PER_DAY
-    if time_unit == "ns":
-        result = s * NS_PER_SECOND
-    elif time_unit == "us":
-        result = s * US_PER_SECOND
-    else:
-        result = s * MS_PER_SECOND
-    return result
+
+
+_TIMESTAMP_DATE_FACTOR: Mapping[TimeUnit, int] = {
+    "ns": NS_PER_SECOND,
+    "us": US_PER_SECOND,
+    "ms": MS_PER_SECOND,
+    "s": 1,
+}
+
+
+def calculate_timestamp_date(s: NativeSeriesT, time_unit: TimeUnit) -> NativeSeriesT:
+    return s * SECONDS_PER_DAY * _TIMESTAMP_DATE_FACTOR[time_unit]
 
 
 def select_columns_by_name(