<!---------------add code in function.php ------------------>

<?php

add_filter( 'the_content', 'time_ago' );

function time_ago ( $content ) {

$content .= "

" . __( 'Posted ', 'test' ) . human_time_diff( get_the_time('U'), current_time('timestamp') ) . __( ' ago', 'test' );

return $content;

}

?>