The DLC is basically guaranteed to give you +1100 War Assets if you complete all three DLC stories. If you complete everything in Mass Effect 3 singleplayer, you’ll only be able to earn 3750 war assets total.

By completing all the DLC before initiating the final battle on Earth, you’ll be able to earn a lot of extra War Assets. Mass Effect: Legendary Edition doesn’t include multiplayer or any of the other external methods for earning War Assets - but it does include all the bonus DLC. To get the best possible ending - as in, you’ll actually get an ending at all - you’ll need to collect 3100 War Assets. If you don’t reach a high enough Readiness Rating, Shephard and his team will die during the final confrontation with the Reapers.

By making the tough choices in main story missions or in side-quests, you can earn more War Assets that go to your total Readiness Rating. To unlock all possible endings in Mass Effect 3, you’ll need to participate in the Readiness Rating System - an all-encompassing rating of your War Assets that determines how well your army fairs in the final battle against the Reapers.

Mass effect 3 how to get best ending