Taxes Calculator

tax_change_graph.py

#!/usr/bin/env python

# This snippet generates a chart showing tax changes after China's 2011 Individual Income Tax Adjustment Draft.
# Both NumPy & PyLab are required here. Please make sure you have these libs installed.

import sys

from pylab import arange, array, frompyfunc, plot, show
from taxes import NEW_THRESHOLD, NEW_TAX_LEVELS, OLD_THRESHOLD, OLD_TAX_LEVELS, income_tax


def income_tax_ufunc(threshold, tax_levels):
    def income_tax_func(income):
        return income_tax(income, threshold=threshold, tax_levels=tax_levels)
    return frompyfunc(income_tax_func, 1, 1)


new_income_tax_ufunc = income_tax_ufunc(threshold=NEW_THRESHOLD, tax_levels=NEW_TAX_LEVELS)
old_income_tax_ufunc = income_tax_ufunc(threshold=OLD_THRESHOLD, tax_levels=OLD_TAX_LEVELS)


if __name__ == '__main__':
    try:
        if len(sys.argv) == 1:
            maximum = 50000.
        else:
            _, maximum = sys.argv
            maximum = float(maximum)
    except ValueError:
        print >>sys.stderr, '%s: invalid maximum income value' % sys.argv[0]
        sys.exit(1)
    x = arange(0., maximum, 1000.)
    y = new_income_tax_ufunc(x) - old_income_tax_ufunc(x)
    plot([0, maximum], [0, 0])
    plot([0, maximum], [min(y)] * 2)
    plot(x, y, 'o-')
    show()

taxes.py

#!/usr/bin/env python

NEW_HOUSING_FUND_CAP = 12603
OLD_HOUSING_FUND_CAP = 12111

NEW_INSURANCE_CAP    = 12603
OLD_INSURANCE_CAP    = 12111

NEW_TAX_LEVELS  = ((0.05, 0), (0.1, 75), (0.2, 525), (0.25, 975), (0.3, 2725), (0.35, 5475), (0.45, 13475))
OLD_TAX_LEVELS  = ((0.05, 0), (0.1, 25), (0.15, 125), (0.2, 375), (0.25, 1375), (0.3, 3375), (0.35, 6375), (0.4, 10375), (0.45, 15375))

NEW_THRESHOLD       = 3000
OLD_THRESHOLD       = 2000

HOUSING_FUND_RATE   = 0.12
HOUSING_FUND_CAP    = NEW_HOUSING_FUND_CAP
INSURANCE_RATES     = (
    (0.08, 0),      # Pension
    (0.02, 3),      # Medical
    (0.002, 0),     # Unemployment
)
INSURANCE_CAP       = NEW_INSURANCE_CAP
TAX_LEVELS          = NEW_TAX_LEVELS
THRESHOLD           = NEW_THRESHOLD


def income_tax(income, threshold, tax_levels):
    deduced = income - threshold
    return round(max(0, *(deduced * rate - qcd for (rate, qcd) in tax_levels)), 2)


def housing_fund(pretax_income, cap, rate):
    base = min(pretax_income, cap)
    return round(base * rate, 2)


def insurances(pretax_income, cap, rates):
    base = min(pretax_income, cap)
    return round(sum([base * rate + extra for (rate, extra) in rates]), 2)


def post_tax_income(pretax_income, threshold, tax_levels, housing_fund_cap, housing_fund_rate, insurance_cap, insurance_rates):
    result = pretax_income
    result -= housing_fund(pretax_income, housing_fund_cap, housing_fund_rate)
    result -= insurances(pretax_income, insurance_cap, insurance_rates)
    result -= income_tax(result, threshold, tax_levels)
    return round(result, 2)


if __name__ == '__main__':
    def post_tax_income_2011(pretax_income):
        return post_tax_income(pretax_income, threshold=THRESHOLD, tax_levels=TAX_LEVELS, housing_fund_cap=HOUSING_FUND_CAP, housing_fund_rate=HOUSING_FUND_RATE, insurance_cap=INSURANCE_CAP, insurance_rates=INSURANCE_RATES)
    import sys
    try:
        _, income = sys.argv
        income = float(income)
    except ValueError:
        print >> sys.stderr, "%s: income value required" % sys.argv[0]
        sys.exit(-1)
    h = housing_fund(income, cap=HOUSING_FUND_CAP, rate=HOUSING_FUND_RATE)
    i = insurances(income, cap=INSURANCE_CAP, rates=INSURANCE_RATES)
    report = (
        ('Pre-tax Income', income),
        ('Deduced Housing Fund', h),
        ('Deduced Insurances', i),
        ('Pre-tax Income with Social Insurances off', income - h - i),
        ('Individual Income Tax', income_tax(income - h - i, THRESHOLD, TAX_LEVELS)),
        ('Post Tax Income', post_tax_income_2011(income)),
        ('Post Tax Income with Housing Funds', post_tax_income_2011(income) + 2 * h),
    )
    title_length = max([len(title) for title, _ in report])
    title_length = (title_length + 5) / 4 * 4
    format = '%%-%ds%%9.2f' % title_length
    for title, value in report:
        print format % (title + ':', value)

Output please