Baker's Dozen

A direct result of medieval English law. The Assize of Bread and Ale, enacted in 1266, set strict weight standards for loaves sold to the public, with severe fines, or worse, for bakers caught selling underweight bread. Since it was hard to guarantee every loaf's exact weight by hand, bakers routinely threw in a thirteenth loaf, sometimes called the "vantage loaf," free of charge, as a buffer against being caught short and punished.