austax: Implement calculation of mandatory study loan repayment

austax/__init__.py

@@ -21,9 +21,7 @@ from drcr.database import db
 import drcr.plugins
 from drcr.webapp import app
 
-from .reports import tax_summary_report
-
-from datetime import datetime
+from .reports import eofy_date, tax_summary_report
 
 def plugin_init():
 	drcr.plugins.advanced_reports.append(('/tax/summary', 'Tax summary'))
@@ -46,9 +44,7 @@ def make_tax_transactions():
 	tax_amount = report.by_id('total_tax').amount
 	
 	# Get EOFY date
-	dt = datetime.now().replace(month=6, day=30)
-	if dt < datetime.now():
-		dt = dt.replace(year=dt.year + 1)
+	dt = eofy_date()
 	
 	# Estimated tax payable
 	transactions = [Transaction(
@@ -60,6 +56,18 @@ def make_tax_transactions():
 		]
 	)]
 	
+	# Mandatory study loan repayment
+	loan_repayment = report.by_id('loan_repayment').amount
+	if loan_repayment.quantity != 0:
+		transactions.append(Transaction(
+			dt=dt,
+			description='Mandatory study loan repayment payable',
+			postings=[
+				Posting(account='HELP', quantity=loan_repayment.quantity, commodity='$'),  # FIXME: Correct account
+				Posting(account='Income Tax Control', quantity=-loan_repayment.quantity, commodity='$')
+			]
+		))
+	
 	# Get trial balance
 	balancer = TrialBalancer()
 	balancer.apply_transactions(db.session.scalars(db.select(Transaction).options(db.selectinload(Transaction.postings))).all())

austax/reports.py

@@ -14,22 +14,34 @@
 #   You should have received a copy of the GNU Affero General Public License
 #   along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
+from drcr import AMOUNT_DPS
 from drcr.database import db
 from drcr.models import AccountConfiguration, Amount, Transaction, TrialBalancer
 from drcr.reports import Calculated, Report, Section, Spacer, Subtotal, entries_for_kind
 
-def base_income_tax(taxable_income):
-	income = taxable_income.quantity
+from .tax_tables import base_tax, repayment_rates
 
-	if income <= 1820000:
-		return Amount(0, '$')
-	if income <= 4500000:
-		return Amount(int((income - 1820000) * 0.19), '$')
-	if income <= 12000000:
-		return Amount(int(509200 + (income - 4500000) * 0.325), '$')
-	if income <= 18000000:
-		return Amount(int(2946700 + (income - 12000000) * 0.37), '$')
-	return Amount(int(5166700 + (income - 18000000) * 0.45), '$')
+from datetime import datetime
+
+def eofy_date(dt=None):
+	"""Get the datetime for the end of the financial year"""
+	
+	if dt is None:
+		dt = datetime.now()
+	
+	dt_eofy = dt.replace(month=6, day=30)
+	if dt_eofy < dt:
+		dt_eofy = dt_eofy.replace(year=dt.year + 1)
+	
+	return dt_eofy
+
+def base_income_tax(year, taxable_income):
+	"""Get the amount of base income tax"""
+	
+	for i, (upper_limit, flat_amount, marginal_rate) in enumerate(base_tax[year]):
+		if upper_limit is None or taxable_income.quantity <= upper_limit * (10**AMOUNT_DPS):
+			lower_limit = base_tax[year][i - 1][0]
+			return Amount(flat_amount * (10**AMOUNT_DPS) + marginal_rate * (taxable_income.quantity - lower_limit * (10**AMOUNT_DPS)), '$')
 
 def medicare_levy(taxable_income):
 	if taxable_income.quantity < 2920700:
@@ -37,10 +49,16 @@ def medicare_levy(taxable_income):
 	
 	return Amount(int(taxable_income.quantity * 0.02), '$')
 
+def study_loan_repayment(year, taxable_income):
+	"""Get the amount of mandatory study loan repayment"""
+	
+	for upper_limit, rate in repayment_rates[year]:
+		if upper_limit is None or taxable_income.quantity <= upper_limit * (10**AMOUNT_DPS):
+			return Amount(rate * taxable_income.quantity, '$')
+
 def tax_summary_report():
 	# Get trial balance
 	balancer = TrialBalancer()
-	#balancer.apply_transactions(all_transactions())
 	balancer.apply_transactions(db.session.scalars(db.select(Transaction).options(db.selectinload(Transaction.postings))).all())
 	
 	accounts = dict(sorted(balancer.accounts.items()))
@@ -100,7 +118,7 @@ def tax_summary_report():
 					entries=[
 						Calculated(
 							'Base income tax',
-							lambda _: base_income_tax(report.by_id('taxable').amount)
+							lambda _: base_income_tax(eofy_date().year, report.by_id('taxable').amount)
 						),
 						Calculated(
 							'Medicare levy',
@@ -116,8 +134,14 @@ def tax_summary_report():
 				),
 				Spacer(),
 				Calculated(
-					'Income tax payable (refundable)',
-					lambda _: report.by_id('total_tax').amount - report.by_id('paygw').amount,
+					'Mandatory study loan repayment',
+					lambda _: study_loan_repayment(eofy_date().year, report.by_id('taxable').amount),
+					id='loan_repayment'
+				),
+				Spacer(),
+				Calculated(
+					'ATO liability payable (refundable)',
+					lambda _: report.by_id('total_tax').amount - report.by_id('paygw').amount + report.by_id('loan_repayment').amount,
 					heading=True,
 					bordered=True
 				)

austax/tax_tables.py

@@ -0,0 +1,55 @@
+#   DrCr: Web-based double-entry bookkeeping framework
+#   Copyright (C) 2022–2023  Lee Yingtong Li (RunasSudo)
+#
+#   This program is free software: you can redistribute it and/or modify
+#   it under the terms of the GNU Affero General Public License as published by
+#   the Free Software Foundation, either version 3 of the License, or
+#   (at your option) any later version.
+#
+#   This program is distributed in the hope that it will be useful,
+#   but WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#   GNU Affero General Public License for more details.
+#
+#   You should have received a copy of the GNU Affero General Public License
+#   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+# Base income tax
+# https://www.ato.gov.au/rates/individual-income-tax-rates/
+# Maps each financial year to list of (upper limit (INclusive), flat amount, marginal rate)
+base_tax = {
+	2023: [
+		(18200, 0, 0),
+		(45000, 0, 0.19),
+		(120000, 5092, 0.325),
+		(180000, 29467, 0.37),
+		(None, 51667, 0.45)
+	]
+}
+
+# Study and training loan (HELP, etc.) repayment thresholds and rates
+# https://www.ato.gov.au/Rates/HELP,-TSL-and-SFSS-repayment-thresholds-and-rates/
+# Maps each financial year to list of (upper limit (EXclusive), repayment rate)
+repayment_rates = {
+	2023: [
+		(48361, 0),
+		(55837, 0.01),
+		(59187, 0.02),
+		(62739, 0.025),
+		(66503, 0.03),
+		(70493, 0.035),
+		(74723, 0.04),
+		(79207, 0.045),
+		(83959, 0.05),
+		(88997, 0.055),
+		(94337, 0.06),
+		(99997, 0.065),
+		(105997, 0.07),
+		(112356, 0.075),
+		(119098, 0.08),
+		(126244, 0.085),
+		(133819, 0.09),
+		(141848, 0.095),
+		(None, 0.1)
+	]
+}