How long can you keep uncooked lasagna before it spoils?

Cooked meat only keeps 3 days in the fridge: http://www.canfightbac.org/cpcfse/en/cookwell/ask/where_how/#218 If you've got leftovers that you might not want to eat that quickly - freeze them on the day you cook them (chill first). You can always defrost them tomorrow if you need them then.