Temporary hit points last as long as the duration of whatever spell or effect grants them. If a feature that grants temporary hit points does not have a duration, they last until they’re depleted or you finish a long rest.

Temporary hit points are lost first, before you start losing your normal hit points. Once all your temporary hit points are depleted, the remainder of the damage carries over. So if you have 3 temporary hit points and take 5 damage, your temporary hit points are depleted and you take 2 damage.

Temporary hit points don’t stack from multiple sources. If you have them and receive more, you deice whether to keep the ones you have or take the new ones. So if you have 5 temporary hit points and a new effect grants 10, you end up with 10 temporary hit points, not 15.

Player’s Handbook, pg. 198

Matt Zane

Author, DnD Lounge

Matt Zane started DnD Lounge in 2021. Matt began playing DnD 5e in 2015, and has been DMing since 2017. He loves optimization, but also enjoys looking for creative ways to use spells and abilities that follow the spirit and letter of the rules. He also eschews pure optimization in favor of a more balanced approach, where building a character is primarily about serving an interesting story arc and party dynamics rather than maxing out DPR.