Australian Income Tax Calculator

Calculates withheld amounts from gross income as per the Australian Tax Office PAYG (pay-as-you-go) tax tables (currently on the 2018-2019 financial year).

Requirements

• PHP 7.1 or above

If using the included Excel Spreadsheet source reader, you will also need the following PHP extensions enabled:

• ctype
• dom
• gd
• iconv
• fileinfo
• libxml
• mbstring
• SimpleXML
• xml
• xmlreader
• xmlwriter
• zip
• zlib

Installation

Include this library in your application through Composer:

composer require abwebdevelopers/aus-income-tax

Usage

The library requires the published formulas from the Australian Tax Office in order to calculate the withheld amounts from gross income. These are generally published shortly before the end of the financial year. We have provided the latest files in the resources/tax-tables folder.

The codes that the ATO uses are as follows:

Code	Contains
NAT 1004	Standard formula for working out income tax.
NAT 3539	Formula for working out income tax for people who claim a HELP (Higher Education Loan Program), SFSS (Student Financial Supplement Scheme) or other student assistance debt.
NAT 4466	Formula for working out income tax for seniors and pensioners

The easiest way to use this library is to use the Excel Spreadsheet reader to automatically feed this formula into the library:

<?php
use ABWebDevelopers\AusIncomeTax\IncomeTax;
use ABWebDevelopers\AusIncomeTax\Source\ATOExcelSource;

$incomeTax = new IncomeTax(new ATOExcelSource([
    'standardFile' => 'resources/tax-tables/2018-19/NAT_1004_2018.xlsx',
    'helpSfssFile' => 'resources/tax-tables/2018-19/NAT_3539_2018.xlsx',
    'seniorsFile' => 'resources/tax-tables/2018-19/NAT_4466_2018.xlsx'
]));

Once loaded, you can calculate the tax withheld amount of a wage using the following:

$tax = $this->IncomeTax->calculateTax(
    1000,           // The gross wage
    'weekly',       // The pay cycle - must be either `weekly`, `fortnightly`, `monthly` or `quarterly`
    '2018-06-02',   // The payment date
    'standard',     // The type of taxation - either `standard`, `help`, `sfss`, `combo` or `seniors`
     2              // The taxation scale - `1` (tax free threshold not claimed), `2` (tax free threshold claimed), `3` (foreign resident), `4` (no TFN), `5` (full medicare exemption), `5` (half medicare exemption)
);

This should return an integer value of the amount of tax to be withheld for the gross income.

Exception codes

\ABWebDevelopers\AusIncomeTax\Exception\CalculationException

Code	Message
1000	Default error code for calculation errors.
1001	Gross amount cannot be negative.
1002	Invalid payment frequency specified.
2001	Invalid threshold type or scale provided.
2002	No tax table source provided.

\ABWebDevelopers\AusIncomeTax\Exception\SourceException

Code	Message
2000	Default error code for source errors.
2001	Invalid threshold type or scale provided.
2002	Missing or invalid source file provided.
2003	Invalid seniors offset value.
2004	Invalid Medicare Levy Exemption value.
2005	Malformed source file provided.

Disclaimer

Whilst great care has been taken to ensure that this library returns correct withheld tax calculations and has been thoroughly checked against the ATO test data, it does not take into account certain offsets or adjustments that can be made to a person's taxation responsibility. You should always verify any calculations with a registered tax agent. AB Web Developers accepts no responsibility for any tax miscalculations or assumptions that are made as the result of using this library.