Find the cost per egg and per recipe.
Cost per egg is the dozen price divided by twelve, with one adjustment worth making: a few eggs in every carton crack in transit, get dropped, or sit past use. Allowing three percent for that raises the effective cost slightly and makes recipe costing honest. From there the arithmetic compounds fast — a three-egg recipe made four times a week uses over six hundred eggs a year, so the difference between a $2.50 and a $6.50 dozen is more than two hundred dollars annually on that recipe alone. That is the scale at which the premium for free-range or pasture-raised eggs becomes a real budgeting decision rather than a rounding error.
Cost per usable egg and per recipe
Usable fraction = 1 - loss percent / 100; cost per egg = dozen price / (12 x usable fraction); cost per recipe = cost per egg x eggs per recipe; annual = cost per recipe x times per week x 52
Because it is consistent and easy to measure. A single broken egg in a dozen is more than eight percent of the carton, so even a modest allowance is more accurate than assuming perfect usage.
Compare cost per gram rather than per egg. A large egg averages 57 g and an extra-large 64 g, so extra-large is better value only if it costs less than about twelve percent more per dozen.
Within one size, generally yes. Beyond that, weigh instead: recipes are usually written for large eggs at roughly 50 g of edible content, and baking is sensitive enough that two size steps will change the result.