Character condition

Condition can refer to two things — either the condition of the character or (in Fallout 3 and Fallout: New Vegas) the condition of their equipment.

Personal condition
The most common personal conditions found in Fallout 3, Fallout: New Vegas, and Fallout 4 are poisons from Chems or from the environment, and damage from combat. Fallout 4 is currently the only one in the Fallout series to include illnesses.

Other

 * Encumbered
 * Well Rested

Illness
In Fallout 4, the Sole Survivor can become ill in Survival mode.

Illness can commonly be corrected with Antibiotics, being well rested for several days, or by any doctor.

Illness persists for a week and then disappears, but has a chance to persist for another week. Illness contributes to Fatigue and directly impacts Action points. These illnesses are commonly associated with poor sleep and heavy combat. Sleeping for short periods of time to save the game increases the chance of getting an illness, it is good to buff the resistance to the most unwanted effects prior to such a power nap. Using chems, eating uncooked meat, drinking or swimming in irradiated water, and taking damage from feral ghouls, bugs or infected animals — all increase the chances of contracting an ailment.


 * Fatigue - Require more sleep to avoid exhaustion debuffs.
 * Infection - Continuous bleed damage. Similar to poison.
 * Insomnia - 2 more hours of sleep required to stay rested.
 * Lethargy - 50% slower AP regeneration.
 * Parasites - Must eat x2 as much food to avoid hunger.
 * Weakness - Take +20% more damage.

Various Herbal immunostimulants become available for crafting, purchase and as a loot in Survival mode:
 * Herbal stimulant
 * Herbal antimicrobial
 * Herbal anodyne

Equipment condition
Note that any equations are not to be taken as literal representations of what happens in-game, but as accurate, general representations of the logic.

The condition of a weapon or armor directly affects its value and damage for weapon or Damage Threshold for armor, respectively.

If the condition of an item degrades all the way to 0%, the item is broken and cannot be used until repaired. In the case of equipped armor and clothing, bonuses to skills or attributes will still apply even if the item is broken, but once removed it will have to be repaired before it can be re-equipped.

Another consequence of poor condition when using weapons is the reload animation. The lower the condition of a weapon, the more likely it is to jam, causing the player to adjust the magazine, thus taking longer to complete the animation. A weapon at 100% condition will never jam, while weapons in a poor state of repair will jam quite frequently.

Value
The value of an item is calculated by :
 * $$\text{Value} = \text{Base value} \times \text{Condition} ^ {1.5}$$


 * Condition is a number ranging from 0 to 1.

Also, knowing the current value of an item it is possible to find the condition:
 * $$\text{Condition} = \left(\frac{\text{Value}}{\text{Base value}}\right)^\frac{2}{3}$$

For example, the 10mm pistol has a maximum value of 225 caps when in perfect condition. At 50% (or 0.5) condition, the pistol's value is 225 * (0.5 ^ 1.5) = 225 * 0.3535, or 35.3% of its base value (225): 79 caps.

Damage
As condition degrades, non-melee weapon damage will scale linearly from full damage at 100% condition to roughly two-thirds damage at 0% condition for single-shot ranged weapons and roughly half damage for fully-automatic ranged weapons and melee weapons.

\text{Dam}_{\text{Skill}=100}= \text{Base} \times (\text{Minimum} + \text{Condition} \times (1 - \text{Minimum})) $$
 * Condition is a number ranging from 0 to 1.
 * Minimum is .66 for single-shot weapons, .54 for fully-automatic weapons, .5 for melee weapons.

For example, the 10mm pistol has a base damage of 9. At 25% condition and 100 Guns, the pistol's damage would be:
 * $$\text{Dam}_{\text{Guns}=100}=9 \times (.66 + .25 \times .34) = 6.705 \approx 7$$

In another example example, the assault rifle has a base damage of 38. At 25% condition and 100 Guns, the assault rifle's displayed damage would be:
 * $$\text{Dam}_{\text{Guns}=100}=38 \times (.54 + .25 \times .46) = 24.89 \approx 25$$

Armor protection
Armor's damage resistance and Damage Threshold are similarly affected, though skill is not necessary and the value for Minimum is .62:
 * $$\text{DR or DT}=\text{Base} \times (.62 + \text{Condition} \times .38)$$

Equipment degradation
All equipable items in Fallout 3 and Fallout: New Vegas have item health, which helps determine how quickly an item condition degrades from use and from being hit in combat. At full item health, an item is in 100% condition. Similarly, at close to 0 item health, an item is about to break. In Fallout 3, item health decreases per use by a percentage of the base damage of the weapon.
 * Small Guns degrade at 3% of base weapon damage per shot.
 * Energy Weapons degrade at 4% of base weapon damage per shot.
 * Unarmed and Melee Weapons degrade at 5% of base weapon damage per attack.
 * Big Guns degrade at 6% of base weapon damage per shot.

For example, the Plasma rifle has a base damage of 45 and an item health of 900. Each shot will decay the health by 1.8 health, which means that it takes 500 shots to take this plasma rifle from full condition to broken.

Damage
As condition degrades, weapon damage will scale linearly from full damage at 75% condition to half the damage at 0% condition.

\text{Dam}_{\text{Skill}=100}= \text{Base} \times \left(   0.5 + \min      \left( \frac{0.5\times \text{Condition}}{0.75}, 0.5 \right) \right) $$

Armor protection
As condition degrades, armor protection will scale linearly from full protection at 50% condition to about 2/3 of full protection at 0% condition.

\text{DR or DT}=\text{Base} \times \left(   0.66 + \min \left( \frac{0.34\times \text{Condition}}{0.5}, 0.34 \right) \right) $$

Equipment degradation
Weapon condition degrades at a flat rate of 0.2 item health per shot. V.A.T.S. does not impose an additional penalty, but various types of ammunition can increase or decrease the degradation rate (indicated by a "CND x 1.5" or similar in the Pip-Boy 3000, which means a 1.5 multiplier for decay). Having Raul Tejada as a companion can make a weapon degrade slower (a .5 multiplier for Regular Maintenance, a .25 multiplier for Full Maintenance).

Armor condition degrades if an incoming attack power exceeds DT of the armor.