About this tool
The D&D 5e Hit Points Calculator works out a character's maximum HP from three inputs: the class hit die, the level and the Constitution score. Pick your hit-die size (d6 for sorcerers and wizards, d8 for most classes, d10 for fighters, paladins and rangers, or d12 for barbarians), and choose whether levels after the first use the fixed average or the maximum roll. Everything is computed locally in your browser.
At level 1 you get the maximum value of your hit die plus your Constitution modifier, where the modifier is floor((CON − 10) / 2). Each level after the first adds either the fixed average of the die (d6=4, d8=5, d10=6, d12=7) or the die's maximum, plus your Constitution modifier again. So a level-5 fighter (d10) with 14 CON (+2) using fixed averages has 10 + 2 at level 1 and adds 6 + 2 four more times, for 44 HP. Because Constitution is added every level, raising CON retroactively boosts your whole HP total.
Two common HP boosters are built in: the Tough feat adds 2 HP per level, and the Hill Dwarf's Dwarven Toughness racial trait adds 1 HP per level. Toggle either and the total updates. The tool also shows your Constitution modifier, the per-level gain, and your level-1 HP so you can verify the math against your character sheet.