At the end of each day, your character will heal 1 HP for each point of Healing Rate. When you rest, you heal every six hours.In-game description
Initial Level: Starting healing rate is equal to 1/3 Endurance, with a minimum of 1. Average characters will have a healing rate of 1.
Healing rate in New Vegas is set according to a character's Endurance stat. An Endurance of 9 or 10 gives a healing rate of 10, Endurance 6-8 gives a healing rate of 5, and Endurance 5 or less gives no healing rate at all. Each point of healing rate restores 0.066HP per in-game hour, which translates to 1HP every three hours for a rate of 5, and 2HP every three hours for a rate of 10. The effect is applied in real-time, during waiting, and while sleeping in Hardcore mode.