After reading and joining a recent Twitter conversation about the complexity of the XP and CR system in 5th edition D&D, it dawned on me that I could throw together a quick Excel sheet to calculate XP for the encounter, XP per PC, and encounter difficulty, according to the current rules (Basic Rules for DMs v. 0.1).
Click here to download the Fifth Edition Encounter Calculator version 0.1. It's designed for parties of 3-5 PCs. UPDATE 12/18/14: See below for an even better one someone else made.
Note: This is an MS Excel document shared through Google Drive, so you have to download it to edit it. It's shared for personal use only, not commercial use. It contains game information from the D&D Basic Rules for 5th edition, available for free from Wizards of the Coast, here.
Edit 9/1/14: With this update, I clarified that the XP multiplier on p.57 is only used to assess challenge, not XP reward for the PCs. I provided the XP per PC for awarding just the XP from the monsters (no multiplier) as the default and created a field for awarding XP based on the actual encounter difficulty -- which I had to calculate anyway, to calculate the challenge level.
Edit 12/18/14: There's a better encounter calculator out there that's better than what I made. I won't keep you away from a better option just to get more clicks. This is the best 5e encounter calculator I've found: http://kobold.club/fight/#/encounter-builder