fix: Monthly depreciation using WDV method

erpnext/assets/doctype/asset/asset.py

@@ -257,6 +257,7 @@ class Asset(AccountsController):
 				number_of_pending_depreciations += 1
 
 			skip_row = False
+			should_get_last_day = is_last_day_of_the_month(finance_book.depreciation_start_date)
 
 			for n in range(start[finance_book.idx - 1], number_of_pending_depreciations):
 				# If depreciation is already completed (for double declining balance)
@@ -270,6 +271,9 @@ class Asset(AccountsController):
 						finance_book.depreciation_start_date, n * cint(finance_book.frequency_of_depreciation)
 					)
 
+					if should_get_last_day:
+						schedule_date = get_last_day(schedule_date)
+
 					# schedule date will be a year later from start date
 					# so monthly schedule date is calculated by removing 11 months from it
 					monthly_schedule_date = add_months(schedule_date, -finance_book.frequency_of_depreciation + 1)
@@ -845,14 +849,9 @@ class Asset(AccountsController):
 			if args.get("rate_of_depreciation") and on_validate:
 				return args.get("rate_of_depreciation")
 
-			no_of_years = (
-				flt(args.get("total_number_of_depreciations") * flt(args.get("frequency_of_depreciation")))
-				/ 12
-			)
 			value = flt(args.get("expected_value_after_useful_life")) / flt(self.gross_purchase_amount)
 
-			# square root of flt(salvage_value) / flt(asset_cost)
-			depreciation_rate = math.pow(value, 1.0 / flt(no_of_years, 2))
+			depreciation_rate = math.pow(value, 1.0 / flt(args.get("total_number_of_depreciations"), 2))
 
 			return 100 * (1 - flt(depreciation_rate, float_precision))
 
@@ -1103,9 +1102,18 @@ def is_cwip_accounting_enabled(asset_category):
 def get_total_days(date, frequency):
 	period_start_date = add_months(date, cint(frequency) * -1)
 
+	if is_last_day_of_the_month(date):
+		period_start_date = get_last_day(period_start_date)
+
 	return date_diff(date, period_start_date)
 
 
+def is_last_day_of_the_month(date):
+	last_day_of_the_month = get_last_day(date)
+
+	return getdate(last_day_of_the_month) == getdate(date)
+
+
 @erpnext.allow_regional
 def get_depreciation_amount(asset, depreciable_value, row):
 	if row.depreciation_method in ("Straight Line", "Manual"):

erpnext/assets/doctype/asset/test_asset.py

@@ -701,6 +701,39 @@ class TestDepreciationMethods(AssetSetup):
 		asset.reload()
 		self.assertEquals(asset.finance_books[0].value_after_depreciation, 98000.0)
 
+	def test_monthly_depreciation_by_wdv_method(self):
+		asset = create_asset(
+			calculate_depreciation=1,
+			available_for_use_date="2022-02-15",
+			purchase_date="2022-02-15",
+			depreciation_method="Written Down Value",
+			gross_purchase_amount=10000,
+			expected_value_after_useful_life=5000,
+			depreciation_start_date="2022-02-28",
+			total_number_of_depreciations=5,
+			frequency_of_depreciation=1,
+		)
+
+		expected_schedules = [
+			["2022-02-28", 645.0, 645.0],
+			["2022-03-31", 1206.8, 1851.8],
+			["2022-04-30", 1051.12, 2902.92],
+			["2022-05-31", 915.52, 3818.44],
+			["2022-06-30", 797.42, 4615.86],
+			["2022-07-15", 384.14, 5000.0],
+		]
+
+		schedules = [
+			[
+				cstr(d.schedule_date),
+				flt(d.depreciation_amount, 2),
+				flt(d.accumulated_depreciation_amount, 2),
+			]
+			for d in asset.get("schedules")
+		]
+
+		self.assertEqual(schedules, expected_schedules)
+
 
 class TestDepreciationBasics(AssetSetup):
 	def test_depreciation_without_pro_rata(self):
@@ -787,7 +820,7 @@ class TestDepreciationBasics(AssetSetup):
 		expected_values = [["2020-12-31", 30000.0], ["2021-12-31", 30000.0], ["2022-12-31", 30000.0]]
 
 		for i, schedule in enumerate(asset.schedules):
-			self.assertEqual(expected_values[i][0], schedule.schedule_date)
+			self.assertEqual(getdate(expected_values[i][0]), schedule.schedule_date)
 			self.assertEqual(expected_values[i][1], schedule.depreciation_amount)
 
 	def test_set_accumulated_depreciation(self):
@@ -1261,6 +1294,32 @@ class TestDepreciationBasics(AssetSetup):
 		asset.cost_center = "Main - _TC"
 		asset.submit()
 
+	def test_depreciation_on_final_day_of_the_month(self):
+		"""Tests if final day of the month is picked each time, if the depreciation start date is the last day of the month."""
+
+		asset = create_asset(
+			item_code="Macbook Pro",
+			calculate_depreciation=1,
+			purchase_date="2020-01-30",
+			available_for_use_date="2020-02-15",
+			depreciation_start_date="2020-02-29",
+			frequency_of_depreciation=1,
+			total_number_of_depreciations=5,
+			submit=1,
+		)
+
+		expected_dates = [
+			"2020-02-29",
+			"2020-03-31",
+			"2020-04-30",
+			"2020-05-31",
+			"2020-06-30",
+			"2020-07-15",
+		]
+
+		for i, schedule in enumerate(asset.schedules):
+			self.assertEqual(getdate(expected_dates[i]), getdate(schedule.schedule_date))
+
 
 def create_asset_data():
 	if not frappe.db.exists("Asset Category", "Computers"):