calculate-percentage.php

<?php

//add custom callback to calculate the percentage between two fields//

add_filter( 'jet-engine-calculated-callback/config', function( $callbacks = array() ) {

  $callbacks['calculate_percent_callback'] = function( $field_value, $fields ) {

    $additional_field = jet_engine()->listings->data->get_meta( $fields );

    if ( $field_value <= 0 || $additional_field <= 0 ) {

      return;

    }

     $result = ( 1 - $field_value / $additional_field );

     $result = $result * 100;

    return $result;

  };

  return $callbacks;

});