Hit Point Rolls
Players should keep track of their hit point rolls at each level on their character sheet.
If a character’s hit point total is below the hit point total that they would have if they had rolled the average rounded down at each level, then their hit point total is replaced with the latter for that level. Note that the rolls do not change, and that this is rechecked at each level.
1. At level 2, Jack the fighter takes another level of fighter. He rolls a 2/10. Because the average-rounded-down calculation of 10+5=15 is lower than the actual rolls of 10+2=12, he uses 15 as the base, pre-Con hit point total at level 2.
2. At level 3, Jack the fighter rolls a 10/10. He keeps his roll of 2 from level 2, and now his rolls are 10+2+10=22 as compared with the average rounded down calculation of 10+5+5=20. So now Jack uses 22 as his base, pre-Con hit point total at level 3.
3. At level 4, Jack takes a level of Barbarian. He is unlucky and rolls a 1/12.
Hit point rolls = 10+2+10+1=23
Average-rounded-down calculation = 10+5+5+6=26
So Jack uses 26 as his base hit point total before adding Con bonus.