diff --git a/conservancy_beancount/cliutil.py b/conservancy_beancount/cliutil.py
index cc2f5deddd32f8827c7b9702f4324e5c9b62dca7..22167f977e0f513f49d0721b3ebcb1fbf6a09ea6 100644
--- a/conservancy_beancount/cliutil.py
+++ b/conservancy_beancount/cliutil.py
@@ -255,6 +255,17 @@ def add_version_argument(parser: argparse.ArgumentParser) -> argparse.Action:
 def date_arg(arg: str) -> datetime.date:
     return datetime.datetime.strptime(arg, '%Y-%m-%d').date()
 
+def diff_year(date: datetime.date, diff: int) -> datetime.date:
+    new_year = date.year + diff
+    try:
+        return date.replace(year=new_year)
+    except ValueError:
+        # The original date is Feb 29, which doesn't exist in the new year.
+        if diff < 0:
+            return datetime.date(new_year, 2, 28)
+        else:
+            return datetime.date(new_year, 3, 1)
+
 def year_or_date_arg(arg: str) -> Union[int, datetime.date]:
     """Get either a date or a year (int) from an argument string
 
diff --git a/conservancy_beancount/reports/fund.py b/conservancy_beancount/reports/fund.py
index c21e4358198e90db5bcdf9ed9c839d1d588e3b8a..90df1ffe74130047712a00e69803a17f245f897c 100644
--- a/conservancy_beancount/reports/fund.py
+++ b/conservancy_beancount/reports/fund.py
@@ -339,17 +339,6 @@ metadata to match. A single ticket number is a shortcut for
             args.report_type = ReportType.ODS
     return args
 
-def diff_year(date: datetime.date, diff: int) -> datetime.date:
-    new_year = date.year + diff
-    try:
-        return date.replace(year=new_year)
-    except ValueError:
-        # The original date is Feb 29, which doesn't exist in the new year.
-        if diff < 0:
-            return datetime.date(new_year, 2, 28)
-        else:
-            return datetime.date(new_year, 3, 1)
-
 def main(arglist: Optional[Sequence[str]]=None,
          stdout: TextIO=sys.stdout,
          stderr: TextIO=sys.stderr,
@@ -365,9 +354,9 @@ def main(arglist: Optional[Sequence[str]]=None,
         if args.start_date is None:
             args.stop_date = datetime.date.today()
         else:
-            args.stop_date = diff_year(args.start_date, 1)
+            args.stop_date = cliutil.diff_year(args.start_date, 1)
     if args.start_date is None:
-        args.start_date = diff_year(args.stop_date, -1)
+        args.start_date = cliutil.diff_year(args.stop_date, -1)
 
     returncode = 0
     books_loader = config.books_loader()
diff --git a/conservancy_beancount/reports/ledger.py b/conservancy_beancount/reports/ledger.py
index 6297e0efd0bc3ac3deaaf58f5db2c4ad4750b115..05df5507ec7227f1a7854a922291d511da0f926b 100644
--- a/conservancy_beancount/reports/ledger.py
+++ b/conservancy_beancount/reports/ledger.py
@@ -747,17 +747,6 @@ metadata to match. A single ticket number is a shortcut for
             args.accounts = list(LedgerODS.ACCOUNT_COLUMNS)
     return args
 
-def diff_year(date: datetime.date, diff: int) -> datetime.date:
-    new_year = date.year + diff
-    try:
-        return date.replace(year=new_year)
-    except ValueError:
-        # The original date is Feb 29, which doesn't exist in the new year.
-        if diff < 0:
-            return datetime.date(new_year, 2, 28)
-        else:
-            return datetime.date(new_year, 3, 1)
-
 def main(arglist: Optional[Sequence[str]]=None,
          stdout: TextIO=sys.stdout,
          stderr: TextIO=sys.stderr,
@@ -771,11 +760,11 @@ def main(arglist: Optional[Sequence[str]]=None,
 
     today = datetime.date.today()
     if args.start_date is None:
-        args.start_date = diff_year(today, -1)
+        args.start_date = cliutil.diff_year(today, -1)
         if args.stop_date is None:
             args.stop_date = today + datetime.timedelta(days=30)
     elif args.stop_date is None:
-        args.stop_date = diff_year(args.start_date, 1)
+        args.stop_date = cliutil.diff_year(args.start_date, 1)
 
     returncode = 0
     books_loader = config.books_loader()
diff --git a/tests/test_cliutil.py b/tests/test_cliutil.py
index f26c4884b1b12c1be9fb228fa79c7a22e7bcb17c..5a558d88fb0745fe0815e64ca0df50252c63931e 100644
--- a/tests/test_cliutil.py
+++ b/tests/test_cliutil.py
@@ -218,3 +218,21 @@ def test_version_argument(argparser, capsys, arg):
     stdout, _ = capsys.readouterr()
     lines = iter(stdout.splitlines())
     assert re.match(r'^test_cliutil version \d+\.\d+\.\d+', next(lines, "<EOF>"))
+
+@pytest.mark.parametrize('date,diff,expected', [
+    (datetime.date(2010, 2, 28), 0, datetime.date(2010, 2, 28)),
+    (datetime.date(2010, 2, 28), 1, datetime.date(2011, 2, 28)),
+    (datetime.date(2010, 2, 28), 2, datetime.date(2012, 2, 28)),
+    (datetime.date(2010, 2, 28), -1, datetime.date(2009, 2, 28)),
+    (datetime.date(2010, 2, 28), -2, datetime.date(2008, 2, 28)),
+    (datetime.date(2012, 2, 29), 2, datetime.date(2014, 3, 1)),
+    (datetime.date(2012, 2, 29), 4, datetime.date(2016, 2, 29)),
+    (datetime.date(2012, 2, 29), -2, datetime.date(2010, 2, 28)),
+    (datetime.date(2012, 2, 29), -4, datetime.date(2008, 2, 29)),
+    (datetime.date(2010, 3, 1), 1, datetime.date(2011, 3, 1)),
+    (datetime.date(2010, 3, 1), 2, datetime.date(2012, 3, 1)),
+    (datetime.date(2010, 3, 1), -1, datetime.date(2009, 3, 1)),
+    (datetime.date(2010, 3, 1), -2, datetime.date(2008, 3, 1)),
+])
+def test_diff_year(date, diff, expected):
+    assert cliutil.diff_year(date, diff) == expected