How is incoming damage calculated in Fallout 4?

Solution 1:

You can refer to Fallout's wikia article on damage resistance to understand how damage is calculated in Fallout 4.

The damage coeffecient looks like this

but the ultimate damage is determined as:

But there are a lot of types of damage such as explosive, poison, energy and radiation. It is essential to check the linked wikia article for a comprehensive explanation of how all types of damage are calculated.

As for your question of how the game handles weapons that fire multiple types of damage, this too is answered in the wikia article:

"When something has multiple resistible damage types ... one "hit" resolves as a hit for each damage type applied. Likewise, when something deals both direct and area of effect damage, a target is hit by each one individually. For example... a fully charged shot from the weapon will inflict 6 distinct "hits": energy damage, explosive energy damage, explosive projectile damage, radiation damage, explosive radiation damage and radiation poisoning."

In regards to additional questions in the comments: Incoming damage of two types from one attack qualifies as two distinct calculations- one for each damage type. Energy and explosive are distinct, but there are weapons that can deal two or more types of damage in the same shot such as the Radium Rifle (27 damage ballistic, 50 damage radiation). Again, this is still calculated as two distinct attacks: one calculation for the ballistic damage and a second for the radiation damage.

Regardless, the calculation for each damage type is identical, explosive damage uses the same formula as ballistic damage uses the same formula as energy, etc. The damage type determine what perks take effect and what your armor blocks against. Some damage types, such as poison, have additional effects that only apply after the damage calculation is performed.

As for radiation specifically: Each point of radiation damage you receive removes .1% of your overall health. If you receive ten points of damage from a Gamma Gun your health will be reduced by ten points and your maximum health cap will be reduced by 1%.