diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index bb893bd2ffef6..bfa560ccae068 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -4566,7 +4566,7 @@ def shift(self, periods=1, freq=None):
         """
         raise NotImplementedError(f"Not supported for type {type(self).__name__}")
 
-    def argsort(self, *args, **kwargs):
+    def argsort(self, *args, **kwargs) -> np.ndarray:
         """
         Return the integer indices that would sort the index.
 
@@ -5052,7 +5052,7 @@ def _searchsorted_monotonic(self, label, side="left"):
 
         raise ValueError("index must be monotonic increasing or decreasing")
 
-    def get_slice_bound(self, label, side, kind):
+    def get_slice_bound(self, label, side, kind) -> int:
         """
         Calculate slice bound that corresponds to given label.
 
@@ -5217,7 +5217,7 @@ def delete(self, loc):
         """
         return self._shallow_copy(np.delete(self._data, loc))
 
-    def insert(self, loc, item):
+    def insert(self, loc: int, item):
         """
         Make new Index inserting new item at location.
 
diff --git a/pandas/core/indexes/category.py b/pandas/core/indexes/category.py
index a247a986fcb55..a7afa78190d90 100644
--- a/pandas/core/indexes/category.py
+++ b/pandas/core/indexes/category.py
@@ -798,7 +798,7 @@ def delete(self, loc):
         """
         return self._create_from_codes(np.delete(self.codes, loc))
 
-    def insert(self, loc, item):
+    def insert(self, loc: int, item):
         """
         Make new Index inserting new item at location. Follows
         Python list.append semantics for negative values
diff --git a/pandas/core/indexes/interval.py b/pandas/core/indexes/interval.py
index 4df1d25c7ff0c..1b851ca38459a 100644
--- a/pandas/core/indexes/interval.py
+++ b/pandas/core/indexes/interval.py
@@ -468,7 +468,7 @@ def is_unique(self):
         return True
 
     @property
-    def is_overlapping(self):
+    def is_overlapping(self) -> bool:
         """
         Return True if the IntervalIndex has overlapping intervals, else False.
 
@@ -562,7 +562,7 @@ def _can_reindex(self, indexer: np.ndarray) -> None:
         if self.is_overlapping and len(indexer):
             raise ValueError("cannot reindex from an overlapping axis")
 
-    def _needs_i8_conversion(self, key):
+    def _needs_i8_conversion(self, key) -> bool:
         """
         Check if a given key needs i8 conversion. Conversion is necessary for
         Timestamp, Timedelta, DatetimeIndex, and TimedeltaIndex keys. An
@@ -1036,7 +1036,7 @@ def _format_space(self) -> str:
 
     # --------------------------------------------------------------------
 
-    def argsort(self, *args, **kwargs):
+    def argsort(self, *args, **kwargs) -> np.ndarray:
         return np.lexsort((self.right, self.left))
 
     def equals(self, other) -> bool:
diff --git a/pandas/core/indexes/multi.py b/pandas/core/indexes/multi.py
index 21421a6f6ea62..10a2d9f68a7b6 100644
--- a/pandas/core/indexes/multi.py
+++ b/pandas/core/indexes/multi.py
@@ -2013,7 +2013,7 @@ def append(self, other):
         except (TypeError, IndexError):
             return Index(new_tuples)
 
-    def argsort(self, *args, **kwargs):
+    def argsort(self, *args, **kwargs) -> np.ndarray:
         return self.values.argsort(*args, **kwargs)
 
     @Appender(_index_shared_docs["repeat"] % _index_doc_kwargs)
@@ -3135,7 +3135,7 @@ def equals(self, other) -> bool:
 
         return True
 
-    def equal_levels(self, other):
+    def equal_levels(self, other) -> bool:
         """
         Return True if the levels of both MultiIndex objects are the same
 
@@ -3335,7 +3335,7 @@ def _convert_can_do_setop(self, other):
             result_names = self.names if self.names == other.names else None
         return other, result_names
 
-    def insert(self, loc, item):
+    def insert(self, loc: int, item):
         """
         Make new MultiIndex inserting new item at location
 
diff --git a/pandas/core/indexes/numeric.py b/pandas/core/indexes/numeric.py
index 53f96ace890fb..2638784f7b50d 100644
--- a/pandas/core/indexes/numeric.py
+++ b/pandas/core/indexes/numeric.py
@@ -160,7 +160,7 @@ def is_all_dates(self) -> bool:
         return False
 
     @Appender(Index.insert.__doc__)
-    def insert(self, loc, item):
+    def insert(self, loc: int, item):
         # treat NA values as nans:
         if is_scalar(item) and isna(item):
             item = self._na_value
diff --git a/pandas/core/indexes/range.py b/pandas/core/indexes/range.py
index 1629396796b85..67eb5c26fc83a 100644
--- a/pandas/core/indexes/range.py
+++ b/pandas/core/indexes/range.py
@@ -421,7 +421,7 @@ def max(self, axis=None, skipna=True, *args, **kwargs):
         nv.validate_max(args, kwargs)
         return self._minmax("max")
 
-    def argsort(self, *args, **kwargs):
+    def argsort(self, *args, **kwargs) -> np.ndarray:
         """
         Returns the indices that would sort the index and its
         underlying data.
@@ -441,7 +441,7 @@ def argsort(self, *args, **kwargs):
         else:
             return np.arange(len(self) - 1, -1, -1)
 
-    def equals(self, other):
+    def equals(self, other) -> bool:
         """
         Determines if two Index objects contain the same elements.
         """
diff --git a/pandas/tseries/frequencies.py b/pandas/tseries/frequencies.py
index e2d007cd2d7f8..af34180fb3170 100644
--- a/pandas/tseries/frequencies.py
+++ b/pandas/tseries/frequencies.py
@@ -334,7 +334,7 @@ def is_unique(self) -> bool:
         return len(self.deltas) == 1
 
     @cache_readonly
-    def is_unique_asi8(self):
+    def is_unique_asi8(self) -> bool:
         return len(self.deltas_asi8) == 1
 
     def get_freq(self) -> Optional[str]: