Since so many people seem to forget here is a reminder:

At 1st level you get the full HP for your class plus Con bonus plus any additional HP you would gain as a result of additional Feats:

eg: a first level Fighter with a Constitution of 14 and the Improved Toughness Feat would start with 10 + 2 + 1 = 13 HP.

Every Even level you gain Class HP/2 plus Con bonus plus any additional HP you would gain as a result of additional Feats:

eg: The same Fighter taking a second level of fighter would have 13 + 5 + 2 +1 for a total of 20 HP.

Every ODD level other than first you gain Class HP/2 +1 plus Con bonus plus any additional HP you would gain as a result of additional Feats:

eg: The same Fighter taking a third level of fighter would have 20 + 6 + 2 + 1 for a total of 29 HP

The additional HP comes on ODD levels not even. If you guys could try to keep that straight it would make level ups a bit less confusing.

Thank you,

Kemian