Round Down

Unless a rule says otherwise, fractions are rounded down when computing game values.

Standard cases:

• Hit point thresholds for Bloodied (half HP, round down) and various features that trigger at "half" something
• Half cover, three-quarters cover computed bonuses on saves
• Half damage on a successful save for spells like fireball — a roll of 23 damage becomes 11 on a save, not 12
• Resistance (half damage rounded down) — 7 damage with resistance becomes 3
• Vulnerability (double damage) — no rounding needed; multiply first, round only if a subsequent halving applies
• Ability score modifiers — these are computed as (score − 10) / 2, round down, which is why a score of 13 yields a +1 modifier, not +1.5
• Spell slot recovery, hit dice spent, healing surges — round down on fractions

Exceptions where rules round up:

• A handful of features explicitly say "round up" (some optional rules, certain class features in expanded books)
• Proficiency Bonus is whole-number by character level; no rounding needed
• XP thresholds for advancement are whole numbers in the published tables

Why round down is the default: It is the simplest and most predictable rule. When in doubt, round down; if you remember an exception, it will say so on the page.