The easy way to go about it is, treat first level as if you’d rolled max HP, and subsequent levels as if you’d rolled one over half of the die’s maximum.  So, on a d8, it would be 8+5+5+5, for example.  Apply your CON modifier (and other relevant modifiers) to each “roll.”<br/><br/>Also, for the group in the game, all this talk about having one group take the frontal assault path with two others sneak around behind them, I already have<a class="postlink" href="https://www.youtube.com/watch?v=waa2ucfgVgQ">this</a>playing in my head.