diff --git a/doc/api/next_api_changes/deprecations/26894-AL.rst b/doc/api/next_api_changes/deprecations/26894-AL.rst
new file mode 100644
index 000000000000..b156fa843917
--- /dev/null
+++ b/doc/api/next_api_changes/deprecations/26894-AL.rst
@@ -0,0 +1,6 @@
+*interval* parameter of ``TimerBase.start``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Setting the timer *interval* while starting it is deprecated.  The interval can
+be specified instead in the timer constructor, or by setting the
+``timer.interval`` attribute.
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
index cdca80df0c82..a411cfbe3a4a 100644
--- a/lib/matplotlib/backend_bases.py
+++ b/lib/matplotlib/backend_bases.py
@@ -1117,6 +1117,7 @@ def __del__(self):
         """Need to stop timer and possibly disconnect timer."""
         self._timer_stop()
 
+    @_api.delete_parameter("3.9", "interval", alternative="timer.interval")
     def start(self, interval=None):
         """
         Start the timer object.