I usually just tell my players when to level up, but I am going to start handing out xp again. I am not going to calculate what they should have from what they have done, but the xp they need for 1/3 of a level for instance. Let's say I want the players to level up every three sessions, I will give out 1/3 of the xp they need for next level each session. This way, they get a feeling for when they will level up.