From 0b7d9ef6ee6c3747bb45c4952bbc6cd250018ec7 Mon Sep 17 00:00:00 2001
From: luuhongyii <72600702+luuhongyii@users.noreply.github.com>
Date: Sat, 13 Jun 2026 09:06:17 +0200
Subject: [PATCH] Fix 10Y annualized return window

---
 quantstats/reports.py |  2 +-
 tests/test_reports.py | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/quantstats/reports.py b/quantstats/reports.py
index f0d8a9ad..b82bf0d4 100644
--- a/quantstats/reports.py
+++ b/quantstats/reports.py
@@ -1555,7 +1555,7 @@ def metrics(
         _get_stats().cagr(df[df.index >= d], 0.0, compounded, win_year) * pct
     )
 
-    d = today - relativedelta(years=10)
+    d = today - relativedelta(months=119)
     metrics["10Y (ann.) %"] = (
         _get_stats().cagr(df[df.index >= d], 0.0, compounded, win_year) * pct
     )
diff --git a/tests/test_reports.py b/tests/test_reports.py
index e03bcc97..2001e031 100644
--- a/tests/test_reports.py
+++ b/tests/test_reports.py
@@ -174,6 +174,26 @@ def test_metrics_with_rf(self, sample_returns):
         # Results should be different
         assert not result_no_rf.equals(result_with_rf)
 
+    def test_metrics_10y_annualized_return_uses_partial_month_offset(self):
+        """Test 10Y annualized return uses the same partial-month offset as 3Y/5Y."""
+        dates = pd.date_range("2016-01-31", periods=121, freq="ME")
+        returns = pd.Series(0.01, index=dates, name="Strategy")
+        returns.iloc[0] = -0.50
+
+        result = reports.metrics(
+            returns,
+            display=False,
+            prepare_returns=False,
+            periods_per_year=12,
+        )
+
+        assert result.loc["10Y (ann.)", "Strategy"] == result.loc[
+            "3Y (ann.)", "Strategy"
+        ]
+        assert result.loc["10Y (ann.)", "Strategy"] == result.loc[
+            "5Y (ann.)", "Strategy"
+        ]
+
 
 class TestMatchDates:
     """Test date matching functionality."""