Try following
<your base search which gives http_status field> | stats count as total, count(eval(tonumber(http_status)>499)) as total499plushttpstatus | eval percHttpStatus499Plus = (total499plushttpstatus*100)/total
Try following
<your base search which gives http_status field> | stats count as total, count(eval(tonumber(http_status)>499)) as total499plushttpstatus | eval percHttpStatus499Plus = (total499plushttpstatus*100)/total