Display the discounted percentage near sale price in Single product pages for WC 3.0+

Updated - 2019 (avoid rounding price issue) - 2017 (avoid NAN% percentage value)

woocommerce_sale_price_html hook has been replaced by a different hook in WooCommerce 3.0+, that has now 3 arguments (but not the $product argument anymore).

add_filter( 'woocommerce_format_sale_price', 'woocommerce_custom_sales_price', 10, 3 );function woocommerce_custom_sales_price( $price, $regular_price, $sale_price ) {    // Getting the clean numeric prices (without html and currency)    $_reg_price = floatval( strip_tags($regular_price) );    $_sale_price = floatval( strip_tags($sale_price) );    // Percentage calculation and text    $percentage = round( ( $_reg_price - $_sale_price ) / $_reg_price * 100 ).'%';    $percentage_txt = ' ' . __(' Save ', 'woocommerce' ) . $percentage;    $formatted_regular_price = is_numeric( $regular_price ) ? wc_price( $regular_price ) : $regular_price;    $formatted_sale_price    = is_numeric( $sale_price )    ? wc_price( $sale_price )    : $sale_price;    echo '<del>' . $formatted_regular_price . '</del> <ins>' . $formatted_sale_price . $percentage_txt . '</ins>';}

This code goes in function.php file of your active child theme (or theme) or also in any plugin file.
The code is tested and works. For WooCommerce version 3.0+ (thanks to @Mikebcn and @AsifRao)

For rounding the percentage you can use round(), number_format() or number_format_i18n():

$percentage = number_format_i18n( ( $_reg_price - $_sale_price ) / $_reg_price * 100, 0 ).'%';$percentage = number_format( ( $_reg_price - $_sale_price ) / $_reg_price * 100, 0 ).'%';

Original answer code: Here is that functional similar code:

// Only for WooCommerce version 3.0+add_filter( 'woocommerce_format_sale_price', 'woocommerce_custom_sales_price', 10, 3 );function woocommerce_custom_sales_price( $price, $regular_price, $sale_price ) {    $percentage = round( ( $regular_price - $sale_price ) / $regular_price * 100 ).'%';    $percentage_txt = ' ' . __(' Save ', 'woocommerce' ) . $percentage;    $price = '<del>' . ( is_numeric( $regular_price ) ? wc_price( $regular_price ) : $regular_price ) . '</del> <ins>' . ( is_numeric( $sale_price ) ? wc_price( $sale_price ) . $percentage_txt : $sale_price . $percentage_txt ) . '</ins>';    return $price;}

This code goes in function.php file of your active child theme (or theme) or also in any plugin file.
The code is tested and works. For WooCommerce version 3.0+.