Damage Threshold

Damage Threshold is a combat statistic in Fallout, Fallout 2, and Fallout Tactics: Brotherhood of Steel. It was removed in Fallout 3, leaving Damage Resistance as the only armor statistic. However, it was restored in Fallout: New Vegas.

Fallout: New Vegas
Damage Threshold (DT) is a derived static value that is directly subtracted from the damage of each shot taken. In simple terms if a shot is fired with a damage value of 20 and the target's DT value is 15, then 15 points of damage will be removed from the shot's damage. DT plays an integral part in combination with the target's Damage Resistance (DR) value to determine the amount of final damage inflicted upon the target.

The combined statics of DT and DR (with DT being applied first) determines the total damage reduction applied to each shot, however it should be noted that it is not a simple issue of just subtracting the defined value from the damage of each shot, damage negated in this way will never be reduced below 20% of the weapon's original damage regardless of both DT and DR.
 * $$\max((\text{Shot Damage} - \text{DT}) \times (100\%-\text{DR}\%), (\text{Shot Damage} \times20\%)) = \text{Damage Inflicted}$$

Damage which is reduced to below minimum value is indicated with a shield icon next to the health bar (either the PC, or the non-player character's). When all of an enemy's DT (if it's not 0 to begin with) is overcome with armor piercing attacks, then a broken shield icon will be appear in its place instead. The shield icon is shown during V.A.T.S. and on the HUD's health bars once damage has been inflicted upon a target and will remain for 3 seconds afterwards.

The default value for DT is set at 0, this is then modified mainly by the DT value of Armor and Clothing worn. Other attributes that can also effect the DT value both permanently or temporary of a character are Perks, Traits, Consumables and Ammunition.

Bugs

 * Despite DT being the determining factor for armor in New Vegas, when repairing armor merchants will list DR instead. All armors when viewed from the repair screen have a DR of 0. This is fixed in patch 1.1.1.
 * In the initial release of Fallout: New Vegas, all creatures such as super mutants, robots, or deathclaws had twice as much DT as intended (in other words, twice the amount of DT as was entered in their G.E.C.K. page). This was corrected in the 1.2 patch. A similar bug affects the DR of creatures in Fallout 3 and Fallout: New Vegas, which has not been corrected.
 * In Fallout: New Vegas, the only articles of clothing that provide DR are the Rebreather, which is acquired during the quest Volare!, the Vault 11 jumpsuit, and the scientist outfit.
 * There is a new bug where the DT will not even show up at all.