This is likely an issue with having selected Manual for Hit Point Type before having selected your starting class. If you switch your Hit Point Type to Fixed and back again, it should fix the issue. Alternatively, on the Class section of the Character Builder, you can click Manage HP in the top right, and change Rolled HP from 12 to 10.
I just made a character. It's a fighter with 15 in constitution. I should have 12 HP, but it says my max HP, is 14
Can you link to your affected character sheet so a moderator can review what the problem might be?
This is likely an issue with having selected Manual for Hit Point Type before having selected your starting class. If you switch your Hit Point Type to Fixed and back again, it should fix the issue. Alternatively, on the Class section of the Character Builder, you can click Manage HP in the top right, and change Rolled HP from 12 to 10.
My max hp is 5