Adds custom durations to woocommerce-subscriptions

custom-durations.php

<?php
//* Do NOT include the opening php tag

add_filter( 'woocommerce_subscription_lengths', 'wooninja_custom_subscription_duration' );

/**
 * Filters the subscription lengths available
 * @param  array $ranges the array of ranges (lengths)
 * @return array $ranges the filtered array of ranges (lengths)
 */
function wooninja_custom_subscription_duration( $ranges ) {

 //add a range of 180 days
 $ranges['day'][180] = '180 days';
 //add a range of 104 weeks
 $ranges['week'][104] = '104 weeks';
 //add a range of 36 months
 $ranges['month'][36] = '36 months';
 //add a range of 6 years
 $ranges['year'][6] = '6 years';
 return $ranges;
}