Save Woocomerce discount as percentage to database

With thanks to stillatmylinux for the steer.

Here’s the code I used in the end should anyone need something similar

// Woocommerce Percentage Saved

function percentager_shortcode($atts)
{
// override default attributes with user attributes
$percentager_atts = shortcode_atts([
                                 'reg' => '500',
                                 'sale' => '200'
                             ], $atts);
                             $added_up = round( ( ( $percentager_atts['reg'] - $percentager_atts['sale'] ) / $percentager_atts['reg'] ) * 100 );

// start output
$o = '';

// Words
$o .=  esc_html__($added_up, 'percentager') . '% Off';

// return output
return $o;
}

function percentager_shortcodes_init()
{
add_shortcode('percentager', 'percentager_shortcode');
}

add_action('init', 'percentager_shortcodes_init');

Then the shortcode used in Revolution slider:

[percentager reg=”{{meta:_regular_price}}” sale=”{{meta:_sale_price}}”]