From d92bd5e1a067b2b83a78946dff2cb5c13b68e8d2 Mon Sep 17 00:00:00 2001
From: "Tianlang (Jackie) Chen" <305351710+jackiectl2@users.noreply.github.com>
Date: Fri, 30 Oct 2026 13:56:48 -0400
Subject: [PATCH] Exclude zero polynomial roots from IRR solutions

Trailing zero cash flows can introduce a zero polynomial root, which is converted to an IRR of -1 even though the NPV denominator is undefined there. Require rates to be greater than -1, returning the existing no-solution result when appropriate. Cover both signs, leading zeros, exception mode, valid negative IRRs and batched inputs.

Signed-off-by: Tianlang (Jackie) Chen <305351710+jackiectl2@users.noreply.github.com>
---
 numpy_financial/_financial.py           |  4 ++--
 numpy_financial/tests/test_financial.py | 12 ++++++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/numpy_financial/_financial.py b/numpy_financial/_financial.py
index 1adbbea..6ae42cd 100644
--- a/numpy_financial/_financial.py
+++ b/numpy_financial/_financial.py
@@ -1153,8 +1153,8 @@ def irr(values, *, raise_exceptions=False, selection_logic=_irr_default_selectio
             g = np.roots(row)
             eirr = np.real(g[np.isreal(g)]) - 1
 
-            # Realistic IRR
-            eirr = eirr[eirr >= -1]
+            # The discount factor must be nonzero in the NPV equation.
+            eirr = eirr[eirr > -1]
 
             # If no real solution
             if len(eirr) == 0:
diff --git a/numpy_financial/tests/test_financial.py b/numpy_financial/tests/test_financial.py
index 765e1b2..9a2a0a0 100644
--- a/numpy_financial/tests/test_financial.py
+++ b/numpy_financial/tests/test_financial.py
@@ -796,6 +796,18 @@ def test_numpy_gh_6744(self, v):
         # Test that if there is no solution then npf.irr returns nan.
         assert numpy.isnan(npf.irr(v))
 
+    @pytest.mark.parametrize("cashflows", [
+        [100, 50, 0], [-100, -50, 0], [0, 100, 0], [0, -100, 0],
+    ])
+    def test_zero_polynomial_root_is_not_an_irr(self, cashflows):
+        assert numpy.isnan(npf.irr(cashflows))
+        with pytest.raises(npf.NoRealSolutionError):
+            npf.irr(cashflows, raise_exceptions=True)
+
+    def test_trailing_zeros_preserve_negative_irr(self):
+        assert_allclose(npf.irr([-100, 50, 0, 0]), -0.5)
+        assert_allclose(npf.irr([[-100, 50, 0], [-100, 150, 0]]), [-0.5, 0.5])
+
     def test_gh_15(self):
         v = [
             -3000.0,