I’ll never forget the Thanksgiving when the turkey didn’t finish in time for dinner. As a professional recipe developer, I knew how long to cook a turkey, but my experience must have made me flippant.

It's basically impossible to do if you're just trying to eyeball it. Nearly all of your guests will bring a bigger appetite than usual, piling their plates with turkey and half a dozen side dishes.

Thanksgiving can be a multi-day cooking marathon. All the planning often centers around the main event—that giant, glistening turkey. We’ll tell you what size turkey to buy and how long it needs to ...