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austax: Port full income tax implementation from Python

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RunasSudo 2025-06-02 19:05:57 +10:00
parent 023d1035c5
commit a0071cf120
Signed by: RunasSudo
GPG Key ID: 7234E476BF21C61A
4 changed files with 419 additions and 15 deletions
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85
libdrcr/plugins/austax/calc.luau
View File

@ -20,6 +20,7 @@ local tax_tables = require('../austax/tax_tables')
local calc = {}
-- Get the amount of base income tax
function calc.base_income_tax(net_taxable: number, context: libdrcr.ReportingContext): number
local year, _, _ = libdrcr.parse_date(context.eofy_date)
local base_tax_table = tax_tables.base_tax[year]
@ -36,11 +37,93 @@ function calc.base_income_tax(net_taxable: number, context: libdrcr.ReportingCon
end
if net_taxable <= upper_limit then
return flat_amount + marginal_rate * (net_taxable - lower_limit)
return flat_amount + math.floor(marginal_rate * (net_taxable - lower_limit))
end
end
error('Taxable income not within any tax bracket')
end
-- Get the amount of low income tax offset
-- https://www.ato.gov.au/forms-and-instructions/low-and-middle-income-earner-tax-offsets
-- https://www.austlii.edu.au/cgi-bin/viewdoc/au/legis/cth/consol_act/itaa1997240/s61.115.html
function calc.lito(net_taxable: number, tax_total: number, context: libdrcr.ReportingContext): number
if net_taxable <= 37500 * (10 ^ context.dps) then
-- LITO is non-refundable
-- FIXME: This will not work if we implement multiple non-refundable tax offsets
if tax_total <= 700 * (10 ^ context.dps) then
return tax_total
else
return 700 * (10 ^ context.dps)
end
elseif net_taxable <= 45000 * (10 ^ context.dps) then
return 700 * (10 ^ context.dps) - math.floor(0.05 * (net_taxable - 37500 * (10 ^ context.dps)))
elseif net_taxable <= 66667 * (10 ^ context.dps) then
return 325 * (10 ^ context.dps) - math.floor(0.015 * (net_taxable - 45000 * (10 ^ context.dps)))
else
return 0
end
end
-- Get the amount of Medicare levy
function calc.medicare_levy(net_taxable: number, context: libdrcr.ReportingContext): number
local year, _, _ = libdrcr.parse_date(context.eofy_date)
local threshold_table = tax_tables.medicare_levy_threshold[year]
local lower_threshold = threshold_table[1] * (10 ^ context.dps)
local upper_threshold = threshold_table[2] * (10 ^ context.dps)
if net_taxable < lower_threshold then
return 0
elseif net_taxable < upper_threshold then
-- Medicare levy is 10% of the amount above the lower threshold
return math.floor((net_taxable - lower_threshold) * 0.1)
else
-- Normal Medicare levy
return math.floor(net_taxable * 0.02)
end
end
-- Get the amount of Medicare levy surcharge
function calc.medicare_levy_surcharge(net_taxable: number, rfb_grossedup: number, context: libdrcr.ReportingContext): number
local mls_income = net_taxable + rfb_grossedup
local year, _, _ = libdrcr.parse_date(context.eofy_date)
local mls_table = tax_tables.medicare_levy_surcharge_single[year]
for _, row in ipairs(mls_table) do
local upper_limit = row[1] * (10 ^ context.dps)
local rate = row[2]
if mls_income <= upper_limit then
return math.floor(rate * mls_income)
end
end
error('MLS income not within any MLS bracket')
end
-- Calculate the grossed-up reportable fringe benefit
function calc.rfb_grossup(rfb_taxable: number, context: libdrcr.ReportingContext): number
return math.floor(rfb_taxable * tax_tables.fbt_grossup)
end
-- Get the amount of mandatory study loan repayment
function calc.study_loan_repayment(net_taxable: number, rfb_grossedup: number, context: libdrcr.ReportingContext): number
local repayment_income = net_taxable + rfb_grossedup
local year, _, _ = libdrcr.parse_date(context.eofy_date)
local repayment_table = tax_tables.study_loan_repayment_rates[year]
for _, row in ipairs(repayment_table) do
local upper_limit = row[1] * (10 ^ context.dps)
local rate = row[2]
if repayment_income < upper_limit then
return math.floor(rate * repayment_income)
end
end
error('HELP repayment income not within any repayment bracket')
end
return calc

231
libdrcr/plugins/austax/reporting.luau
View File

@ -111,7 +111,7 @@ function reporting.CalculateIncomeTax.execute(args, context, kinds_for_account,
visible = true,
link = nil,
heading = true,
bordered = true,
bordered = false,
}})
table.insert(report.entries, { Section = section })
table.insert(report.entries, 'Spacer')
@ -159,7 +159,7 @@ function reporting.CalculateIncomeTax.execute(args, context, kinds_for_account,
visible = true,
link = nil,
heading = true,
bordered = true,
bordered = false,
}})
table.insert(report.entries, { Section = section })
table.insert(report.entries, 'Spacer')
@ -202,8 +202,45 @@ function reporting.CalculateIncomeTax.execute(args, context, kinds_for_account,
bordered = false,
}})
-- Medicare levy row
local tax_ml = calc.medicare_levy(net_taxable, context)
if tax_ml ~= 0 then
table.insert(report.entries, { Row = {
text = 'Medicare levy',
quantity = {tax_ml},
id = 'tax_ml',
visible = true,
link = nil,
heading = false,
bordered = false,
}})
end
-- Precompute RFB amount as this is required for MLS
local rfb_taxable = 0
for account, kinds in pairs(kinds_for_account) do
if libdrcr.arr_contains(kinds, 'austax.rfb') then
rfb_taxable -= balances[account] or 0 -- Invert as income = credit balances
end
end
local rfb_grossedup = calc.rfb_grossup(rfb_taxable, context)
-- Medicare levy surcharge row
local tax_mls = calc.medicare_levy_surcharge(net_taxable, rfb_grossedup, context)
if tax_mls ~= 0 then
table.insert(report.entries, { Row = {
text = 'Medicare levy surcharge',
quantity = {tax_mls},
id = 'tax_mls',
visible = true,
link = nil,
heading = false,
bordered = false,
}})
end
-- Total income tax row
local tax_total = tax_base
local tax_total = tax_base + tax_ml + tax_mls
table.insert(report.entries, { Row = {
text = 'Total income tax',
quantity = {tax_total},
@ -213,10 +250,126 @@ function reporting.CalculateIncomeTax.execute(args, context, kinds_for_account,
heading = true,
bordered = true,
}})
table.insert(report.entries, 'Spacer')
-- Generate income tax transaction
-- Low income tax offset row
local offset_lito = calc.lito(net_taxable, tax_total, context)
if offset_lito ~= 0 then
table.insert(report.entries, { Row = {
text = 'Low income tax offset',
quantity = {offset_lito},
id = nil,
visible = true,
link = nil,
heading = false,
bordered = false,
}})
end
-- Total tax offsets row
local offset_total = offset_lito
if offset_total ~= 0 then
table.insert(report.entries, { Row = {
text = 'Total tax offsets',
quantity = {offset_total},
id = nil,
visible = true,
link = nil,
heading = true,
bordered = false,
}})
table.insert(report.entries, 'Spacer')
end
-- Calculate mandatory study loan repayment
local study_loan_repayment = calc.study_loan_repayment(net_taxable, rfb_grossedup, context)
-- Mandatory study loan repayment section
if study_loan_repayment ~= 0 then
-- Taxable value of reportable fringe benefits row
if rfb_taxable ~= 0 then
table.insert(report.entries, { Row = {
text = 'Taxable value of reportable fringe benefits',
quantity = {rfb_taxable},
id = 'rfb_taxable',
visible = true,
link = nil,
heading = false,
bordered = false,
}})
end
-- Grossed-up value row
if rfb_grossedup ~= 0 then
table.insert(report.entries, { Row = {
text = 'Grossed-up value',
quantity = {rfb_grossedup},
id = 'rfb_grossedup',
visible = true,
link = nil,
heading = false,
bordered = false,
}})
end
-- Mandatory study loan repayment row
table.insert(report.entries, { Row = {
text = 'Mandatory study loan repayment',
quantity = {study_loan_repayment},
id = 'study_loan_repayment',
visible = true,
link = nil,
heading = true,
bordered = false,
}})
table.insert(report.entries, 'Spacer')
end
-- Add PAYGW entries
local total_paygw = 0
local entries = entries_for_kind('austax.paygw', false, balances, kinds_for_account)
if #entries ~= 0 then
local section: libdrcr.Section = {
text = 'PAYG withheld amounts',
id = nil,
visible = true,
entries = entries,
}
table.insert(report.entries, { Section = section })
total_paygw = math.floor(entries_subtotal(entries) / 100) * 100
end
-- Total PAYGW row
if total_paygw ~= 0 then
table.insert(report.entries, { Row = {
text = 'Total withheld amounts',
quantity = {total_paygw},
id = 'total_paygw',
visible = true,
link = nil,
heading = true,
bordered = false,
}})
table.insert(report.entries, 'Spacer')
end
-- ATO liability row
local ato_payable = tax_total - offset_total - total_paygw + study_loan_repayment
table.insert(report.entries, { Row = {
text = 'ATO liability payable (refundable)',
quantity = {ato_payable},
id = 'ato_payable',
visible = true,
link = nil,
heading = true,
bordered = true,
}})
-- Generate income tax transactions
local transactions: {libdrcr.Transaction} = {
{
-- # Estimated tax payable
id = nil,
dt = libdrcr.date_to_dt(context.eofy_date),
description = 'Estimated income tax',
@ -226,23 +379,83 @@ function reporting.CalculateIncomeTax.execute(args, context, kinds_for_account,
transaction_id = nil,
description = nil,
account = 'Income Tax',
quantity = tax_total,
quantity = (tax_total - offset_total),
commodity = context.reporting_commodity,
quantity_ascost = tax_total,
quantity_ascost = (tax_total - offset_total),
},
{
id = nil,
transaction_id = nil,
description = nil,
account = 'Income Tax Control',
quantity = -tax_total,
quantity = -(tax_total - offset_total),
commodity = context.reporting_commodity,
quantity_ascost = -tax_total,
}
quantity_ascost = -(tax_total - offset_total),
},
},
},
{
-- Mandatory study loan repayment
id = nil,
dt = libdrcr.date_to_dt(context.eofy_date),
description = 'Mandatory study loan repayment payable',
postings = {
{
id = nil,
transaction_id = nil,
description = nil,
account = 'HELP',
quantity = study_loan_repayment,
commodity = context.reporting_commodity,
quantity_ascost = study_loan_repayment,
},
{
id = nil,
transaction_id = nil,
description = nil,
account = 'Income Tax Control',
quantity = -study_loan_repayment,
commodity = context.reporting_commodity,
quantity_ascost = -study_loan_repayment,
},
},
}
}
-- Transfer PAYGW balances to Income Tax Control
for account, kinds in pairs(kinds_for_account) do
if libdrcr.arr_contains(kinds, 'austax.paygw') then
local balance = balances[account] or 0
if balance ~= 0 then
table.insert(transactions, {
id = nil,
dt = libdrcr.date_to_dt(context.eofy_date),
description = 'PAYG withheld amounts',
postings = {
{
id = nil,
transaction_id = nil,
description = nil,
account = 'Income Tax Control',
quantity = balance,
commodity = context.reporting_commodity,
quantity_ascost = balance,
},
{
id = nil,
transaction_id = nil,
description = nil,
account = account,
quantity = -balance,
commodity = context.reporting_commodity,
quantity_ascost = -balance,
},
},
})
end
end
end
return {
[{ name = 'CalculateIncomeTax', kind = 'Transactions', args = 'VoidArgs' }] = {
Transactions = {

116
libdrcr/plugins/austax/tax_tables.luau
View File

@ -15,10 +15,14 @@
-- 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/>.
local tax_tables = {}
-- Base income tax
-- https://www.ato.gov.au/rates/individual-income-tax-rates/
-- https://www.austlii.edu.au/cgi-bin/viewdoc/au/legis/cth/consol_act/itra1986174/sch7.html
-- https://www.austlii.edu.au/cgi-bin/viewdoc/au/legis/cth/consol_act/itra1986174/s3.html (tax-free threshold)
-- Maps each financial year to list of (upper limit (INclusive), flat amount, marginal rate)
local base_tax = {
tax_tables.base_tax = {
[2025] = {
{18200, 0, 0},
{45000, 0, 0.16},
@ -42,8 +46,114 @@ local base_tax = {
}
}
local tax_tables = {
base_tax = base_tax,
-- FBT type 1 gross-up factor
-- https://www.ato.gov.au/rates/fbt/#GrossupratesforFBT
-- https://www.austlii.edu.au/cgi-bin/viewdoc/au/legis/cth/consol_act/fbtaa1986312/s5b.html
tax_tables.fbt_grossup = 2.0802
-- Medicare levy thresholds
-- https://www.ato.gov.au/Individuals/Medicare-and-private-health-insurance/Medicare-levy/Medicare-levy-reduction/Medicare-levy-reduction-for-low-income-earners/
-- https://www.austlii.edu.au/cgi-bin/viewdoc/au/legis/cth/consol_act/mla1986131/s3.html
-- Maps each financial year to list of (lower threshold, upper threshold)
tax_tables.medicare_levy_threshold = {
[2025] = {27222, 34027},
[2024] = {26000, 32500},
[2023] = {24276, 30345},
[2022] = {23365, 29207}
}
-- Medicare levy surcharge rates (singles)
-- https://www.ato.gov.au/individuals-and-families/medicare-and-private-health-insurance/medicare-levy-surcharge/medicare-levy-surcharge-income-thresholds-and-rates
-- https://www.austlii.edu.au/cgi-bin/viewdb/au/legis/cth/consol_act/mla1986131/s8b.html
-- https://www.austlii.edu.au/cgi-bin/viewdoc/au/legis/cth/consol_act/phia2007248/s22.35.html
-- https://www.austlii.edu.au/cgi-bin/viewdoc/au/legis/cth/consol_act/phia2007248/s22.45.html
-- Maps each financial year to list of (upper limit (INclusive), MLS rate)
-- FIXME: Only supports singles
tax_tables.medicare_levy_surcharge_single = {
[2025] = {
{97000, 0},
{113000, 0.01},
{151000, 0.0125},
{math.huge, 0.015}
},
[2024] = {
{93000, 0},
{108000, 0.01},
{144000, 0.0125},
{math.huge, 0.015}
}
}
-- Study and training loan (HELP, etc.) repayment thresholds and rates
-- https://www.ato.gov.au/Rates/HELP,-TSL-and-SFSS-repayment-thresholds-and-rates/
-- https://www.austlii.edu.au/cgi-bin/viewdoc/au/legis/cth/consol_act/hesa2003271/s154.20.html
-- https://www.austlii.edu.au/cgi-bin/viewdoc/au/legis/cth/consol_act/hesa2003271/s154.25.html
-- https://www.austlii.edu.au/cgi-bin/viewdoc/au/legis/cth/consol_act/hesa2003271/s154.30.html
-- Maps each financial year to list of (upper limit (EXclusive), repayment rate)
tax_tables.study_loan_repayment_rates = {
[2025] = {
{54435, 0},
{62851, 0.01},
{66621, 0.02},
{70619, 0.025},
{74856, 0.03},
{79347, 0.035},
{84108, 0.04},
{89155, 0.045},
{94504, 0.05},
{100175, 0.055},
{106186, 0.06},
{112557, 0.065},
{119310, 0.07},
{126468, 0.075},
{134057, 0.08},
{142101, 0.085},
{150627, 0.09},
{159664, 0.095},
{math.huge, 0.1}
},
[2024] = {
{51550, 0},
{59519, 0.01},
{63090, 0.02},
{66876, 0.025},
{70889, 0.03},
{75141, 0.035},
{79650, 0.04},
{84430, 0.045},
{89495, 0.05},
{94866, 0.055},
{100558, 0.06},
{106591, 0.065},
{112986, 0.07},
{119765, 0.075},
{126951, 0.08},
{134569, 0.085},
{142643, 0.09},
{151201, 0.095},
{math.huge, 0.1}
},
[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},
{math.huge, 0.1}
}
}
return tax_tables

2
libdrcr/src/lib.rs
View File

@ -13,6 +13,4 @@ pub type QuantityInt = i64;
// Magic strings
// TODO: Make this configurable
pub const CURRENT_YEAR_EARNINGS: &'static str = "Current Year Earnings";
pub const INCOME_TAX: &'static str = "Income Tax";
pub const INCOME_TAX_CONTROL: &'static str = "Income Tax Control";
pub const RETAINED_EARNINGS: &'static str = "Retained Earnings";