diff --git a/erpnext/accounts/doctype/subscription_plan/test_subscription_plan.py b/erpnext/accounts/doctype/subscription_plan/test_subscription_plan.py
index 76328f9e4c3..062f924a96f 100644
--- a/erpnext/accounts/doctype/subscription_plan/test_subscription_plan.py
+++ b/erpnext/accounts/doctype/subscription_plan/test_subscription_plan.py
@@ -1,8 +1,58 @@
-# Copyright (c) 2018, Frappe Technologies Pvt. Ltd. and Contributors
+# Copyright (c) 2026, Frappe Technologies Pvt. Ltd. and Contributors
 # See license.txt
 
+import unittest
+
+import frappe
+
+from erpnext.accounts.doctype.subscription_plan.subscription_plan import get_plan_rate
 from erpnext.tests.utils import ERPNextTestSuite
 
 
 class TestSubscriptionPlan(ERPNextTestSuite):
-	pass
+	"""Subscription Plan validates its interval and computes a rate. The Monthly
+	Rate branch multiplies cost by the number of months in the billing window."""
+
+	def setUp(self):
+		frappe.set_user("Administrator")
+
+	def make_plan(self, **args):
+		args = frappe._dict(args)
+		plan = frappe.new_doc("Subscription Plan")
+		plan.plan_name = f"_Test Plan {frappe.generate_hash(length=6)}"
+		plan.item = args.item or "_Test Item"
+		plan.currency = args.currency or "INR"
+		plan.price_determination = args.price_determination
+		plan.cost = args.cost or 0
+		plan.billing_interval = args.billing_interval or "Month"
+		plan.billing_interval_count = (
+			args.billing_interval_count if args.billing_interval_count is not None else 1
+		)
+		return plan
+
+	def test_billing_interval_count_must_be_positive(self):
+		plan = self.make_plan(price_determination="Fixed Rate", cost=100, billing_interval_count=0)
+		self.assertRaises(frappe.ValidationError, plan.insert)
+
+	def test_fixed_rate_applies_prorate_factor(self):
+		plan = self.make_plan(price_determination="Fixed Rate", cost=100)
+		plan.insert()
+		self.assertEqual(get_plan_rate(plan.name), 100)
+		self.assertEqual(get_plan_rate(plan.name, prorate_factor=0.5), 50)
+
+	def test_monthly_rate_within_year(self):
+		plan = self.make_plan(price_determination="Monthly Rate", cost=100)
+		plan.insert()
+		# Jan 1 - Mar 31 is 3 whole months; month-aligned so proration is 0
+		rate = get_plan_rate(plan.name, start_date="2026-01-01", end_date="2026-03-31")
+		self.assertEqual(rate, 300)
+
+	@unittest.expectedFailure
+	def test_monthly_rate_across_year_boundary(self):
+		# SUSPECTED BUG: no_of_months uses relativedelta(end, start).months, which drops
+		# the years component, so a 14-month span (Jan 2026 to Feb 2027) is billed as
+		# just 2 months. Asserts the correct 14-month total; drop the xfail once fixed.
+		plan = self.make_plan(price_determination="Monthly Rate", cost=100)
+		plan.insert()
+		rate = get_plan_rate(plan.name, start_date="2026-01-01", end_date="2027-02-28")
+		self.assertEqual(rate, 1400)