There is another way of making the mortise and tenon joint, and that is by using a loose tenon. This eliminates having to calculate the extra length needed for tenons. Just cut a mortise in both pieces and make a tenon to fit using the router table, equally as strong.
But the easiest and by far the fastest way of cutting loose tenon joints is to invest in a Festool Domino. This machine can cut a day’s worth of mortises in ten minutes! So if productivity is an issue, this is a no brainer.