diff --git a/pyproject.toml b/pyproject.toml
index 29e9bac..d6f0669 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -34,6 +34,7 @@ optional-dependencies.tests = [
   "pyfakefs",
   "pytest",
   "pytest-cov",
+  "time-machine",
 ]
 urls.Changelog = "https://github.com/python/blurb/blob/main/CHANGELOG.md"
 urls.Homepage = "https://github.com/python/blurb"
diff --git a/src/blurb/blurb.py b/src/blurb/blurb.py
index 9950554..dd935c3 100755
--- a/src/blurb/blurb.py
+++ b/src/blurb/blurb.py
@@ -346,6 +346,12 @@ def printable_version(version):
     return version + " final"
 
 
+def format_blurb_filename(section, gh_issue, body, date=None):
+    if date is None:
+        date = sortable_datetime()
+    return f"Misc/NEWS.d/{section}/{date}.gh-issue-{gh_issue}.{nonceify(body)}.rst"
+
+
 class BlurbError(RuntimeError):
     pass
 
diff --git a/tests/test_blurb.py b/tests/test_blurb.py
index e9da901..cfa6d19 100644
--- a/tests/test_blurb.py
+++ b/tests/test_blurb.py
@@ -1,4 +1,5 @@
 import pytest
+import time_machine
 
 from blurb import blurb
 
@@ -176,6 +177,33 @@ def test_printable_version(version, expected):
     assert blurb.printable_version(version) == expected
 
 
+@time_machine.travel("2025-01-07 16:28:41")
+@pytest.mark.parametrize(
+    "date, expected",
+    (
+        (
+            "2025-02-27-01-12-11",
+            "Misc/NEWS.d/Library/2025-02-27-01-12-11.gh-issue-123456.hvsmnR.rst",
+        ),
+        (
+            None,
+            "Misc/NEWS.d/Library/2025-01-07-16-28-41.gh-issue-123456.hvsmnR.rst",
+        ),
+    ),
+)
+def test_format_blurb_filename(date, expected):
+    # Arrange
+    gh_issue = "123456"
+    section = "Library"
+    body = "Hello world!"
+
+    # Act
+    filename = blurb.format_blurb_filename(section, gh_issue, body, date)
+
+    # Assert
+    assert filename == expected
+
+
 @pytest.mark.parametrize(
     "news_entry, expected_section",
     (