Macaroni Salad lasts for 3-4 days after you make it. It’s actually still ok to eat up to a week, but the texture changes, and the tomatoes start to break down. If you are making it way ahead of time, hold off on adding the tomatoes until right before serving.   If the salad seems a little dry you may need to add a tablespoon or two of milk or some additional mayo to get it to the creamy consistency it started out as.