Lifegiver

Livegiver or Life Giver is a perk in Fallout, Fallout 2, Fallout 3, Fallout: New Vegas, Fallout 4, Fallout 76, and Fallout Tactics.

Fallout, Fallout 2, Fallout Tactics
Every time the player character gains a level, they gain an additional four Hit Points for each rank of this perk. With two ranks of Lifegiver, that's +8 HP each level, which is more than 10 points in Endurance would give you.

Although it's not clear from the description, Lifegiver grants +4 HP for every level gained, including the level when the perk was taken. (Fallout Tactics does not give the HP on the level you take the perk.)

Fallout 3, Fallout: New Vegas
You gain an additional 30 Hit Points.

This perk also gives the player character unique dialogue choices when speaking with some specific characters, like Tree Father Birch in Oasis.

Bugs
In Fallout: New Vegas, the health that Lifegiver grants is excluded from the 50% calculation for Ferocious Loyalty.

Effects
This is best as an early-game perk. The math is such that, once one reaches Level 32, they would have been better off just putting 1 more point into Endurance than in getting a level in the Lifegiver perk. However, the benefits of +20 Health early game can be considerable.

The health regeneration gained from the third rank grants the player 0.5% health every second. However, health is not regenerated while in combat (i.e. when enemies are nearby.) The health regeneration is fast enough (out of combat) to be a real convenience.

Effects
Lifegiver is a perk in the Nuclear Winter battle royale mode. It requires 1 SPECIAL point to equip.
 * Nuclear Winter

Fallout 2d20
Increase one's maximum health points by one's Endurance rank.

Each time this perk is taken, the level requirement increases by 5.

Gallery
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