The thouands of feet to lose X 3 plus a few miles to get established in descent and make a gentle level off works well enough as a TOD point. A rate of descent in FPM equal to 5 times your ground speed in knots will keep you aproximately on profile. Add a few more miles if you want to level off early to meet a speed restriction. Works well enough in Jurrasic jets and is a good crosscheck in the robot jets.
Best regards,
Westhawk