diff --git a/doc/changes/dev/14261.newfeature.rst b/doc/changes/dev/14261.newfeature.rst
new file mode 100644
index 00000000000..b4d78ece2e4
--- /dev/null
+++ b/doc/changes/dev/14261.newfeature.rst
@@ -0,0 +1 @@
+Added a ``only_if_changed=True`` parameter to :meth:`mne.Report.save` to skip writing an already up-to-date file, by `Eric Larson`_.
diff --git a/mne/report/report.py b/mne/report/report.py
index 17e1a499682..0323c4da28f 100644
--- a/mne/report/report.py
+++ b/mne/report/report.py
@@ -756,6 +756,7 @@ def open_report(fname, **params):
                 )
         report = Report()
         report.__setstate__(state)
+        report._unsaved_changes = False  # what we have matches what's on disk
     else:
         report = Report(**params)
     # Keep track of the filename in case the Report object is used as a context
@@ -948,6 +949,23 @@ def __init__(
 
         self.fname = None  # The name of the saved report
         self.data_path = None
+        self._unsaved_changes = False  # must come last, mutators set it to True
+
+    @property
+    def unsaved_changes(self):
+        """Whether the report content changed since it was created, loaded, or saved.
+
+        Returns
+        -------
+        unsaved_changes : bool
+            ``True`` if content was added, replaced, removed, or reordered since the
+            report was created, read from disk, or last saved.
+
+        Notes
+        -----
+        .. versionadded:: 1.13
+        """
+        return self._unsaved_changes
 
     @property
     def img_max_width(self):
@@ -1112,7 +1130,9 @@ def copy(self):
         report : instance of Report
             The copied report.
         """
-        return copy.deepcopy(self)
+        report = copy.deepcopy(self)
+        report._unsaved_changes = self._unsaved_changes  # deepcopy uses __setstate__
+        return report
 
     def get_contents(self):
         """Get the content of the report.
@@ -1161,6 +1181,7 @@ def reorder(self, order):
                 f"order must be a permutation of range({n_elements}), got:\n{order}"
             )
         self._content = [self._content[ii] for ii in order]
+        self._unsaved_changes = True
 
     def _content_as_html(self):
         """Generate HTML representations based on the added content & sections.
@@ -1259,6 +1280,7 @@ def add_custom_css(self, css):
         """
         style = f'\n<style type="text/css">\n{css}\n</style>'
         self.include += style
+        self._unsaved_changes = True
 
     def add_custom_js(self, js):
         """Add custom JavaScript to the report.
@@ -1275,6 +1297,7 @@ def add_custom_js(self, js):
         """
         script = f'\n<script type="text/javascript">\n{js}\n</script>'
         self.include += script
+        self._unsaved_changes = True
 
     @fill_doc
     def add_epochs(
@@ -2369,11 +2392,13 @@ def remove(self, *, title=None, tags=None, remove_all=False):
         elif not remove_all:  # only remove last occurrence
             remove_idx = remove_idx[-1]
             del self._content[remove_idx]
+            self._unsaved_changes = True
         else:  # remove all occurrences
             remove_idx = tuple(remove_idx)
             self._content = [
                 e for idx, e in enumerate(self._content) if idx not in remove_idx
             ]
+            self._unsaved_changes = True
 
         return remove_idx
 
@@ -2420,6 +2445,7 @@ def _add_or_replace(self, *, title, section, tags, html_partial, replace=False):
         new_content.dom_id = dom_id
         new_content.html = html_partial(id_=dom_id)
         assert isinstance(new_content.html, str), type(new_content.html)
+        self._unsaved_changes = True
 
     def _add_code(self, *, code, title, language, section, tags, replace):
         if isinstance(code, Path):
@@ -3268,6 +3294,9 @@ def __setstate__(self, state):
             if param_name == "_content":
                 param_val = [_ContentElement(**val) for val in param_val]
             setattr(self, param_name, param_val)
+        # conservative, as we don't know where the state came from (open_report and
+        # copy, which both go through here, set the correct value themselves)
+        self._unsaved_changes = True
         return state
 
     @verbose
@@ -3278,6 +3307,7 @@ def save(
         overwrite=False,
         sort_content=False,
         *,
+        only_if_changed=False,
         verbose=None,
     ):
         """Save the report and optionally open it in browser.
@@ -3305,6 +3335,13 @@ def save(
             -> bem -> forward-solution -> inverse-operator -> source-estimate.
 
             .. versionadded:: 0.24.0
+        only_if_changed : bool
+            If ``True`` and :attr:`~mne.Report.unsaved_changes` is ``False`` and the
+            output file already exists, skip writing it (the existing file is left
+            untouched) and just return its name. If the output file does not exist, it
+            is always written.
+
+            .. versionadded:: 1.13
         %(verbose)s
 
         Returns
@@ -3318,6 +3355,16 @@ def save(
                 warn(f"`data_path` not provided. Using {self.data_path} instead")
             fname = op.join(self.data_path, "report.html")
 
+        if only_if_changed and not self._unsaved_changes:
+            # overwrite="read" so that an existing file is not an error here
+            check_fname = _check_fname(fname, overwrite="read", name=fname)
+            if check_fname.is_file():
+                fname = op.realpath(str(check_fname))
+                logger.info(f"Report has no unsaved changes, not saving to : {fname}")
+                if self.fname is None:
+                    self.fname = fname
+                return fname
+
         fname = str(_check_fname(fname, overwrite=overwrite, name=fname))
         fname = op.realpath(fname)  # resolve symlinks
 
@@ -3367,6 +3414,8 @@ def save(
                 html = [header_html, toc_html, *self.html, footer_html]
                 Path(fname).write_text(data="".join(html), encoding="utf-8")
 
+            self._unsaved_changes = False
+
         building_doc = os.getenv("_MNE_BUILDING_DOC", "").lower() == "true"
         if open_browser and not is_hdf5 and not building_doc:
             webbrowser.open_new_tab("file://" + fname)
diff --git a/mne/report/tests/test_report.py b/mne/report/tests/test_report.py
index 96af2bc37e5..399f19b1978 100644
--- a/mne/report/tests/test_report.py
+++ b/mne/report/tests/test_report.py
@@ -628,9 +628,12 @@ def test_open_report(tmp_path):
     with open_report(hdf5, subjects_dir=tmp_path) as report:
         assert report.subjects_dir == str(tmp_path)
         assert report.fname == str(hdf5)
+        assert not report.unsaved_changes
         report.add_figure(fig=fig1, title="evoked response")
+        assert report.unsaved_changes
     # Exiting the context block should have triggered saving to HDF5
     assert Path(hdf5).exists()
+    assert not report.unsaved_changes
 
     # Let's add some companion data to the HDF5 file
     with h5py.File(hdf5, "r+") as f:
@@ -639,6 +642,7 @@ def test_open_report(tmp_path):
 
     # Load the HDF5 version of the report and check equivalence
     report2 = open_report(hdf5)
+    assert not report2.unsaved_changes
     assert report2.fname == str(hdf5)
     assert report2.subjects_dir == report.subjects_dir
     assert report2.html == report.html
@@ -648,7 +652,9 @@ def test_open_report(tmp_path):
     # Check parameters when loading a report
     pytest.raises(ValueError, open_report, hdf5, foo="bar")  # non-existing
     pytest.raises(ValueError, open_report, hdf5, subjects_dir="foo")
-    open_report(hdf5, subjects_dir=str(tmp_path))  # This should work
+    with open_report(hdf5, subjects_dir=str(tmp_path)) as report3:  # This should work
+        assert not report3.unsaved_changes  # a session that changes nothing ...
+    assert not report3.unsaved_changes  # ... stays clean, though __exit__ still saves
 
     # Check that the context manager doesn't swallow exceptions
     with pytest.raises(ZeroDivisionError):
@@ -688,6 +694,40 @@ def test_remove():
     assert r2.html[2] == r.html[3]
 
 
+def test_unsaved_changes(tmp_path):
+    """Test Report.unsaved_changes and Report.save(only_if_changed=True)."""
+    fname = tmp_path / "report.html"
+    kwargs = dict(open_browser=False, only_if_changed=True)
+    r = Report()
+    assert not r.unsaved_changes
+    fig1, fig2 = _get_example_figures()
+    r.add_figure(fig=fig1, title="figure1")
+    assert r.unsaved_changes
+    assert r.copy().unsaved_changes  # copies inherit the flag
+    # the target does not exist yet, so it's written even though it's up to date
+    assert r.save(fname, **kwargs) == os.path.realpath(fname)
+    assert not r.unsaved_changes
+    content, mtime = fname.read_text("utf-8"), fname.stat().st_mtime_ns
+    # nothing changed, so nothing is written (and no overwrite=True needed)
+    assert r.save(fname, **kwargs) == os.path.realpath(fname)
+    assert (fname.read_text("utf-8"), fname.stat().st_mtime_ns) == (content, mtime)
+    # ... but every kind of content mutation makes it stale again (and get written)
+    for mutate in (
+        lambda: r.add_figure(fig=fig2, title="figure2"),
+        lambda: r.remove(title="figure2"),
+        lambda: r.reorder([0]),
+        lambda: r.add_custom_css("p {color: red;}"),
+        lambda: r.add_custom_js("console.log('hello');"),
+    ):
+        assert not r.unsaved_changes
+        mutate()
+        assert r.unsaved_changes
+        r.save(fname, overwrite=True, **kwargs)
+    assert fname.read_text("utf-8") != content
+    assert r.remove(title="does-not-exist") is None  # no-op, so still up to date
+    assert not r.unsaved_changes
+
+
 @pytest.mark.parametrize("tags", (True, False))  # shouldn't matter
 def test_add_or_replace(tags):
     """Test replacing existing figures in a report."""