130 lines
4.7 KiB
Plaintext
130 lines
4.7 KiB
Plaintext
--!strict
|
|
-- DrCr: Web-based double-entry bookkeeping framework
|
|
-- Copyright (C) 2022-2025 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/>.
|
|
|
|
local libdrcr = require('../libdrcr')
|
|
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]
|
|
|
|
for i, row in ipairs(base_tax_table) do
|
|
local upper_limit = row[1] * (10 ^ context.dps)
|
|
local flat_amount = row[2] * (10 ^ context.dps)
|
|
local marginal_rate = row[3]
|
|
|
|
-- Lower limit is the upper limit of the preceding bracket
|
|
local lower_limit = 0
|
|
if i > 1 then
|
|
lower_limit = base_tax_table[i - 1][1] * (10 ^ context.dps)
|
|
end
|
|
|
|
if net_taxable <= upper_limit then
|
|
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
|