When the target's HP is above 50%, Rehabilitate heals a flat 7 HP.
When the target's HP is below 50% Rehabilitate heals 7 HP + (2 × (50% of Target Maximum HP - Target current HP)).
This can result in situations where the amount of HP restored to the target far exceeds their maximum health. Due to the formula, a target with 7 hp or less will always be healed to max HP, regardless of what that HP maximum is.
A single formula for both cases is:
7 + (2 × (50% of Target Maximum HP - Target current HP), minimum of 0) HP
HP restored table
Bold numbers are numbers where the amount of HP restored would bring the target to full HP.