ca-calc-taxes.php

#!/usr/bin/env php
<?php

$federalRates = [
  [49020, 15],
  [49020, 20.5],
  [53939, 26],
  [64533, 29],
  [216511, 33]
];
$bcRates2021 = [
  [42184, 5.06],
  [84369, 7.7],
  [96866, 10.5],
  [117623, 12.29],
  [159483, 14.7],
  [222420, 16.8],
  [PHP_INT_MAX, 20.5]
];

function f($x) {
  return number_format($x, 2, '.', ',');
}

function federal($salary) {
  global $federalRates;
  $slices = $federalRates;
  $remaining = $salary;
  $tax = 0;
  for ($i = 0; $i < count($slices) && $remaining > 0; $i++) {
    list($slice, $rate) = $slices[$i];
    $amount = min($slice, $remaining);
    $tax += $amount * $rate / 100;
    $remaining -= $amount;
  }
  return [$tax, $salary - $tax];
}

function bc($salary) {
  global $bcRates2021;
  $rates = $bcRates2021;
  $taxed = 0;
  $tax = 0;
  for ($i = 0; $i < count($rates) && $taxed <= $salary; $i++) {
    list($end, $rate) = $rates[$i];
    if ($i === 0) {
      $start = 0;
    } else {
      list($start) = $rates[$i - 1];
    }
    $amount = min($end - $start, $salary - $taxed);
    $taxed += $amount;
    $tax += $amount * $rate / 100;
  }
  return [$tax, $salary - $tax];
}

function owed($salary) {
  list($fdTax) = federal($salary);
  list($bcTax) = bc($salary);
  $total = $fdTax + $bcTax;
  return [$total, $salary - $total];
}

$salary = $argv[1] ?? die("Usage: ${argv[0]} <salary>\n");
list($tax, $after) = owed($salary);
printf("Tax: %s\nSalary after  tax: %s\n", f($tax), f($after));