We each cook 2-3 nights per week. I'd say splitting cooking 50/50 is the default in most families I know unless there are circumstances that prevent it--e.g. one spouse consistently works late, one spouse hates cooking or is an awful cook. (Actually, I really know very few people who hate cooking, and fewer still where there is a mixed cook/non-cook marriage. Most people I know who like to cook end up married to other people who like to cook.)