How does first-level HP work in D&D 5e?

At level 1 you take the maximum of your first class's hit die plus your Constitution modifier. A level 1 Fighter (d10) with +2 CON starts with 10 + 2 = 12 HP. Every level after that follows the rolled or average rule.

What is the difference between max and average HP?

Max HP assumes you take the full hit die on every level-up, which is the absolute ceiling. Average HP uses the fixed value in the rules (half the die plus 1, such as 6 on a d10), which is what most groups use instead of rolling.

How is the average per level calculated?

For a die with X sides, the average gain per level after the first is X divided by 2, plus 1, plus your Constitution modifier. A d8 gives 5 per level, a d10 gives 6, and a d12 gives 7, before adding CON.

How does multiclassing affect HP?

Each class contributes its own hit die per level, but only your very first character level gets the maximum starting roll. Every subsequent level from any class uses the rolled or average value, and your Constitution modifier is added to each.

Does increasing my Constitution modifier raise past HP?

Yes. Constitution applies retroactively to every level. If your CON modifier goes from +2 to +3 at level 8, all eight levels gain 1 HP each, for a total of 8 extra hit points.

What is the D&D Hit Points Calculator?

Enter class hit dice, level, and Constitution modifier to compute maximum HP, average (fixed) HP, and a hit-dice summary for D&D 5e. Supports multiclassing across several classes in one build. It runs free in your browser on Gera Tools, with nothing uploaded.

D&D Hit Points Calculator

Name: D&D Hit Points Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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This calculator gives the two hit-point totals every D&D 5e player needs: the theoretical maximum (full die every level) and the average fixed value most tables actually use. It handles multiclass builds by letting you stack several class rows, and it applies your Constitution modifier to every level.

How it works

Level 1 takes the full first hit die. Every level after that adds either the maximum die (for max HP) or the fixed average. Constitution is added once per character level:

firstLevelHP   = maxDie(class1) + CON
avgPerLevel(d) = (d / 2 + 1) + CON
maxPerLevel(d) = d + CON

totalLevels    = sum of levels across all classes
averageHP      = firstLevelHP + Σ avgPerLevel over the remaining levels
maxHP          = firstLevelHP + Σ maxPerLevel over the remaining levels

The first character level always uses the maximum of its hit die — this is a fixed rule in 5e, not a choice. Multiclassing simply means later levels draw their die size from whichever class you took that level in.

Average HP by hit die size

The fixed average per level (after level 1) uses the formula d/2 + 1:

Hit die	Max per level	Average per level (fixed)
d6 (Wizard, Sorcerer)	6	4
d8 (Cleric, Rogue, Druid, Bard)	8	5
d10 (Fighter, Paladin, Ranger)	10	6
d12 (Barbarian)	12	7

Constitution modifier adds to every level, so a +3 CON modifier on a d10 Fighter gives 13 at level 1 (10 + 3) and 9 per subsequent level (6 + 3).

Single-class worked examples

Level 10 Barbarian (d12), +3 CON:

Level 1: 12 + 3 = 15
Levels 2-10 (9 levels): 9 × (7 + 3) = 9 × 10 = 90
Total average HP: 105 | Max HP: 15 + 9 × 15 = 150

Level 10 Wizard (d6), +1 CON:

Level 1: 6 + 1 = 7
Levels 2-10 (9 levels): 9 × (4 + 1) = 9 × 5 = 45
Total average HP: 52 | Max HP: 7 + 9 × 7 = 70

This difference — 105 versus 52 — illustrates why Barbarians and Wizards feel so different to play even at the same level.

Multiclass example

Fighter 3 / Wizard 2 with +2 CON, starting as Fighter:

Level 1 (Fighter d10): 10 + 2 = 12
Levels 2-3 (Fighter d10, average): 2 × (6 + 2) = 16
Levels 4-5 (Wizard d6, average): 2 × (4 + 2) = 12
Total average HP: 40 | Max HP: 12 + 2×12 + 2×8 = 52

Notice that the Wizard levels contribute notably less HP per level. This is one of the practical trade-offs of dipping into Wizard for spell access.

Tips

The Toughness feat adds 2 HP per character level, which stacks on top of the figure this calculator shows.
An increase to your CON modifier (from an ASI or a magic item) raises HP retroactively for all past levels.
When evaluating a multiclass dip, model the HP cost against the expected benefit using this calculator alongside the multiclass proficiency tracker.