diff --git a/financepy/products/rates/ibor_swap.py b/financepy/products/rates/ibor_swap.py
index 55f5472..37886e4 100644
--- a/financepy/products/rates/ibor_swap.py
+++ b/financepy/products/rates/ibor_swap.py
@@ -330,10 +330,8 @@ class IborSwap:
         while self.fixed_leg.payment_dts[start_index] < value_dt:
             start_index += 1
 
-        # If the swap has yet to settle then we do not include the
-        # start date of the swap as a cpn payment date.
-        if value_dt <= self.effective_dt:
-            start_index = 1
+        # payment_dts contains coupon dates only; the effective date is
+        # not a payment to skip for a forward-starting swap.
 
         # Now PV fixed leg flows.
         flat_pv01 = 0.0
--- /dev/null
+++ b/unit_tests/test_FinIborSwapCashAnnuity.py
@@ -0,0 +1,55 @@
+# Copyright (C) 2026 Xamit Kadirbekov
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+import math
+import pytest
+
+from financepy.market.curves.discount_curve_flat import DiscountCurveFlat
+from financepy.models.black import Black
+from financepy.products.rates.ibor_swap import IborSwap
+from financepy.products.rates.ibor_swaption import IborSwaption
+from financepy.utils.calendar import BusDayAdjustTypes
+from financepy.utils.date import Date
+from financepy.utils.day_count import DayCountTypes
+from financepy.utils.frequency import FrequencyTypes
+from financepy.utils.global_types import SwapTypes
+
+
+FREQUENCIES = [(1, FrequencyTypes.ANNUAL), (2, FrequencyTypes.SEMI_ANNUAL),
+               (4, FrequencyTypes.QUARTERLY), (12, FrequencyTypes.MONTHLY)]
+VALUE_DATE = Date(15, 1, 2026)
+START_DATE = Date(15, 1, 2027)
+
+
+def make_swap(m, frequency, periods):
+    return IborSwap(START_DATE, START_DATE.add_months(periods * (12 // m)),
+                    SwapTypes.PAY, 0.04, frequency, DayCountTypes.THIRTY_E_360,
+                    bd_type=BusDayAdjustTypes.NONE)
+
+
+@pytest.mark.parametrize('m,frequency', FREQUENCIES)
+@pytest.mark.parametrize('periods', [1, 5])
+def test_zero_rate_annuity_counts_every_future_payment(m, frequency, periods):
+    swap = make_swap(m, frequency, periods)
+    assert len(swap.fixed_leg.payment_dts) == periods
+    assert swap.cash_settled_pv01(VALUE_DATE, 0.0, frequency) == pytest.approx(periods / m)
+
+
+@pytest.mark.parametrize('m,frequency', FREQUENCIES)
+def test_three_payments_at_positive_rate(m, frequency):
+    swap = make_swap(m, frequency, 3)
+    expected = sum((1 / m) / (1 + 0.04 / m)**j for j in [1, 2, 3])
+    assert swap.cash_settled_pv01(START_DATE, 0.04, frequency) == pytest.approx(expected)
+
+
+@pytest.mark.parametrize('side', [SwapTypes.PAY, SwapTypes.RECEIVE])
+def test_one_payment_cash_swaption_has_positive_black_value(side):
+    option = IborSwaption(VALUE_DATE, START_DATE, START_DATE.add_years(1), side,
+                         0.04, FrequencyTypes.ANNUAL, DayCountTypes.THIRTY_E_360,
+                         notional=1e6, bd_type=BusDayAdjustTypes.NONE)
+    curve = DiscountCurveFlat(VALUE_DATE, 0.03)
+    # ATM Black price: F * (2*Phi(sigma*sqrt(T)/2)-1), for T=1.
+    black_price = 0.04 * math.erf(0.25 / (2 * math.sqrt(2)))
+    expected = 1e6 * math.exp(-0.03) * black_price / 1.04
+    actual = option.cash_settled_value(VALUE_DATE, curve, 0.04, Black(0.25))
+    assert actual == pytest.approx(expected, abs=0.02)