Hit Chance is the likelihood that you will successfully hit a target in combat. It depends on a number of things, including the weapon, the distance to the target, the skill of the shooter, the armor class of the target and more. The final hit chance can never be more than 95%, or 90% if you have the Fast Shot trait.
Hand-to-Hand weapons always have a 95% (90% with fast shot) chance to hit, except if you are blinded or disoriented, in which case it's 50%.
For ranged weapons there are two important thresholds for calculating the hit chance. The first one is related to the "effective range", which is defined for each weapon as 2/3 of the maximum range of that weapon. So a weapon with a max range of 60, will have an effective range of 40. Shooting at a target inside the effective range will generally be easy and require little skill. Shooting at targets beyond the effective range will require a lot of skill, the farther you shoot, the more skill will be required.
The second threshold is related to the skill. With 150 skill, you will be "proficient" with a weapon, meaning your hit chance is 95% at the effective range of the weapon (2/3 of max range). Each skill point above 150 will allow you to shoot an extra 0.4% of the effective range.
Base Hit Chance
Your base hit chance with a ranged weapon is given by your skill with that weapon. With 50 skill, you have 95 hit chance, and for each additional skill point up to 150, you get another 0.95 hit chance, so that with 150 skill, you have 190 hit chance. Every skill point above 150 gives 4 extra hit chance, so that with the ma
For each skill point in a weapon skill, you will gain some Base Hit Chance. If your target is closer than 2/3 of the weapon's max range, you will get a further bonus to the base hit chance, otherwise you will get a penalty to the hit chance.
Your final hit chance will then become the base hit chance, minus a number of situational penalties, that will be described below.
Base Hit Chance Formula
The formula for the base hit chance is given by:
Skill below 150:
baseHitChance = 0.95*(skill-50) + rangeModifier
Skill above 150:
baseHitChance = 95 + (skill-150)*4 + rangeModifier
The range modifier is given by:
Distance to target less than effectiveRange:
rangeModifier = 95*(effectiveRange - distanceToTarget)/effectiveRange
Distance to target greater than effectiveRange:
rangeModifier = 1000*(effectiveRange - distanceToTarget)/effectiveRange
effectiveRange = 2*maxRange/3
Interpretation of the base hit chance
With 50 skill, your hit chance is 95% at 0 distance. With 150 skill, your hit chance is 95% at effective range (2/3 of max range). For each skill point above 150 skill, you can shoot an additional 0.4% of the effective range.
Example: Weapon with 150 max range has an effective range of 100. With 150 skill, you can shoot at 100 range with 95% hit chance. With 160 skill, you can shoot at 104 range, with 95% hit chance. With 250 skill (which is max skill), you can shoot at 140 range with 95% hit chance. At 141 range, your hit chance is 85%, at 142 range, it's 75%, etc.. At 149 range, hit chance is 5%, with max skill.
Penalties to hit chance
Your final hit chance against a target is based on the Base Hit Chance discussed above, but there are many potential penalties to this calculation. The penalties are also slightly different for burst and single shot weapons.
All weapons require a minimum strength to use properly. Not meeting this requirement will affect your final hit chance. Each strength point missing from the strength requirement of the weapon will cost 40 hit chance.
For burst fire, strength is also required to handling the recoil properly. For this reason, having less than 10 strength gives an additional penalty of 10 to the final hit chance.
The weapon handling perk gives +2 strength for the purposes of this check.
So for example, if your strength is 4, shooting a weapon with a strength requirement of 6 will cost 80 hit chance if firing single shots, and 80+60=140 hit chance if firing bursts.
The strength penalty is reduced to 10 if your weapon skill is less than 150.
Having a low perception affects your hit chance with all ranged weapons. For each perception point below 5, you will have a penalty of 40 to your final hit chance, or 10 if your skill was less than 150. This affects both burst and single shot. The Sharpshooter perk gives +2 perception for this check.
Blinded and Disoriented
Knocked out targets
If the target is knocked out, you get +50 hit chance.
If you're shooting single shots, your final hit chance is affected by the armor class of the target, if it has any. A target only has armor class while running, and the amount is determined by agility, luck, armor, traits and perks. The amount is further modified by the ammunition used by the shooter, as well as possible weapon perks.
The amount is given by the following formula:
acPenalty = AC*(22 - Perception)/4
Only single shots can be aimed shots. Depending on which body part you aim for, you will get a penalty to the final hit chance. Note that eye shots will be automatically changed to head shots if you are shooting a target from behind.
The cost to hit chance is given by:
aimPenalty = aim*(15-Perception)
where aim is a number depending on where you aimed:
Eyes: aim = 20
Head: aim = 13
Groin : aim = 10
Arms: aim = 10
Legs: aim = 10
Torso: aim = 0