Secret Lesson 26

Resistance, Vulnerability, and Immunity

In Lesson 25, you learned that every instance of damage has a:

DAMAGE TYPE

You also learned that Damage Types do not create special rules by themselves.

Instead, other mechanics refer to those Damage Types.

Three of the most important are:

RESISTANCE

VULNERABILITY

and:

IMMUNITY

These rules determine whether a creature or object takes:

  • reduced damage

  • increased damage

  • no damage at all

from a particular Damage Type.

PART ONE — RESISTANCE

Some creatures and objects have:

RESISTANCE

to one or more Damage Types.

If you have Resistance to a Damage Type:

DAMAGE OF THAT TYPE IS HALVED AGAINST YOU

and the result is:

ROUNDED DOWN

 

BASIC RESISTANCE FORMULA

DAMAGE ÷ 2

ROUND DOWN

EXAMPLE — EVEN DAMAGE

You have:

RESISTANCE TO COLD DAMAGE

You take:

20 Cold damage

Calculation:

20 ÷ 2 = 10

Final damage:

10 COLD DAMAGE

EXAMPLE — ODD DAMAGE

You have Resistance to Cold.

Incoming damage:

15

Half:

7.5

Round down:

7 DAMAGE

The SRD explicitly requires Resistance to be:

ROUNDED DOWN

 

RESISTANCE APPLIES TO THE SPECIFIED DAMAGE TYPE

If you have:

FIRE RESISTANCE

that does not automatically provide:

  • Cold Resistance

  • Lightning Resistance

  • Acid Resistance

  • Resistance to every other Damage Type

The rule protects you from the Damage Type specified by the Resistance.

EXAMPLE

You have:

RESISTANCE TO FIRE DAMAGE

You take:

18 Fire damage

Final:

9 FIRE DAMAGE

Later you take:

18 Lightning damage

Your Fire Resistance doesn't modify that Lightning damage.

RESISTANCE TO ALL DAMAGE

A rule can also provide:

RESISTANCE TO ALL DAMAGE

The SRD uses this form of Resistance in its example explaining how multiple Resistances interact.

When such a rule applies, use it according to its wording.

RESISTANCE DOES NOT MEAN IMMUNITY

Resistance reduces the relevant damage.

It does not normally reduce it to zero.

For example:

Incoming damage:

12

Resistance:

12 ÷ 2

=

6 DAMAGE

The creature is still taking damage.

RESISTANCE AND 1 DAMAGE

What if the incoming damage is:

1

Resistance halves it:

1 ÷ 2 = 0.5

Round down:

0 DAMAGE

So Resistance can sometimes reduce a very small amount of damage to zero because the rule specifically tells you to halve and round down.

PART TWO — VULNERABILITY

Vulnerability works in the opposite direction.

If you have:

VULNERABILITY TO A DAMAGE TYPE

damage of that type is:

DOUBLED AGAINST YOU

 

BASIC VULNERABILITY FORMULA

DAMAGE × 2

EXAMPLE — FIRE VULNERABILITY

You have:

VULNERABILITY TO FIRE DAMAGE

Incoming Fire damage:

12

Calculation:

12 × 2

=

24 FIRE DAMAGE

EXAMPLE — SMALL DAMAGE

Incoming damage:

3

Vulnerability:

3 × 2

=

6 DAMAGE

VULNERABILITY APPLIES ONLY TO THE RELEVANT TYPE

Suppose a creature has:

VULNERABILITY TO FIRE

It takes:

10 Cold damage

Fire Vulnerability doesn't modify that damage.

But if it later takes:

10 Fire damage

the Fire damage becomes:

20

under the Vulnerability rule.

RESISTANCE VS. VULNERABILITY

The easiest way to remember them is:

Defense Effect
Resistance Halve the damage, round down
Vulnerability Double the damage

 

PART THREE — NO STACKING

This is one of the most important rules in the entire system.

Multiple instances of:

RESISTANCE

to the same Damage Type do:

NOT STACK

Likewise, multiple instances of:

VULNERABILITY

to the same Damage Type do:

NOT STACK

The SRD says that multiple instances affecting the same Damage Type count as:

ONLY ONE INSTANCE

 

TWO RESISTANCES DO NOT QUARTER THE DAMAGE

Suppose you somehow have:

  • Resistance to Necrotic damage from one source

  • another Resistance to Necrotic damage from another source

Incoming Necrotic damage:

20

You do not calculate:

20 → 10 → 5

Instead:

APPLY RESISTANCE ONCE

20 → 10

Final:

10 NECROTIC DAMAGE

SRD EXAMPLE — OVERLAPPING RESISTANCES

The SRD specifically gives an example of a creature that has:

RESISTANCE TO NECROTIC DAMAGE

and:

RESISTANCE TO ALL DAMAGE

When it takes Necrotic damage, those two Resistances don't halve the damage twice.

Necrotic damage is reduced:

BY HALF ONCE

 

WHY?

Because both Resistance effects apply to:

THE SAME INSTANCE OF NECROTIC DAMAGE

and the No Stacking rule says they count as:

ONE INSTANCE OF RESISTANCE

MULTIPLE VULNERABILITIES ALSO DON'T STACK

Suppose two different features somehow give a creature:

VULNERABILITY TO FIRE

Incoming Fire damage:

10

You do not calculate:

10 → 20 → 40

Instead:

APPLY VULNERABILITY ONCE

Final:

20

because multiple Vulnerabilities affecting the same Damage Type count as only one instance.

PART FOUR — RESISTANCE AND VULNERABILITY TOGETHER

A creature can potentially have both:

RESISTANCE

and:

VULNERABILITY

applying to the same incoming damage.

When this happens, the SRD tells us exactly:

IN WHAT ORDER TO APPLY THEM

This is extremely important.

ORDER OF APPLICATION

Damage modifiers are applied in this order:

1. ADJUSTMENTS

such as:

  • bonuses

  • penalties

  • multipliers

2. RESISTANCE

3. VULNERABILITY

 

THE ORDER MATTERS

Do not freely choose the sequence.

The SRD explicitly establishes:

ADJUSTMENTS FIRST

then:

RESISTANCE

then:

VULNERABILITY

 

SRD WORKED EXAMPLE

The SRD gives a very useful example.

A creature has:

RESISTANCE TO ALL DAMAGE

and:

VULNERABILITY TO FIRE DAMAGE

It is also within a magical aura that:

REDUCES ALL DAMAGE BY 5

The creature takes:

28 FIRE DAMAGE

Let's resolve it exactly in the required order.

STEP 1 — APPLY THE DAMAGE ADJUSTMENT

Starting damage:

28

Magical aura:

−5

Calculation:

28 − 5

=

23

STEP 2 — APPLY RESISTANCE

Current damage:

23

Resistance halves it:

23 ÷ 2 = 11.5

Round down:

11

STEP 3 — APPLY VULNERABILITY

Current damage:

11

Vulnerability doubles it:

11 × 2

=

22

Final damage:

22 FIRE DAMAGE

This is the exact sequence demonstrated by the SRD.

COMPLETE FORMULA

For the SRD example:

28 FIRE

↓

−5 ADJUSTMENT

=

23

↓

RESISTANCE

23 ÷ 2 = 11.5

round down:

11

↓

VULNERABILITY

11 × 2

=

22 FINAL DAMAGE

WHY DOESN'T RESISTANCE + VULNERABILITY SIMPLY CANCEL?

It can be tempting to assume:

half × double = original number

But rounding can change the result.

The SRD's example demonstrates exactly this.

Original after adjustment:

23

Half and round down:

11

Double:

22

So the final result is:

22

not 23.

That is why the correct order of operations matters.

ANOTHER EXAMPLE — EVEN NUMBER

Suppose after all initial adjustments you have:

20 FIRE DAMAGE

Target has:

  • Fire Resistance

  • Fire Vulnerability

Resistance:

20 ÷ 2 = 10

Vulnerability:

10 × 2 = 20

Final:

20

With an even number, the two effects can mathematically return the damage to its previous amount.

ODD NUMBER EXAMPLE

Damage:

19

Resistance:

19 ÷ 2 = 9.5

Round down:

9

Vulnerability:

9 × 2

=

18

Final:

18

Again, rounding matters.

PART FIVE — IMMUNITY

The strongest of these protections is:

IMMUNITY

The SRD recognizes Immunity to:

DAMAGE TYPES

and:

CONDITIONS

 

DAMAGE IMMUNITY

If you have Immunity to a Damage Type:

YOU TAKE NO DAMAGE OF THAT TYPE

 

EXAMPLE — FIRE IMMUNITY

Incoming damage:

30 FIRE

Target has:

IMMUNITY TO FIRE DAMAGE

Damage taken:

0

IMMUNITY IS NOT RESISTANCE

Resistance:

HALVES DAMAGE

Immunity:

PREVENTS DAMAGE OF THAT TYPE

Compare:

Incoming Fire damage:

20

Fire Resistance

10 DAMAGE

Fire Immunity

0 DAMAGE

CONDITION IMMUNITY

The SRD also allows creatures and objects to have:

IMMUNITY TO CONDITIONS

If you have Immunity to a condition:

YOU AREN'T AFFECTED BY THAT CONDITION

 

EXAMPLE — POISONED IMMUNITY

Suppose an effect attempts to give a creature:

THE POISONED CONDITION

If that creature has:

IMMUNITY TO THE POISONED CONDITION

it isn't affected by that condition.

DAMAGE IMMUNITY AND CONDITION IMMUNITY ARE SEPARATE CONCEPTS

This connects to Lesson 25.

Remember:

POISON DAMAGE

and:

THE POISONED CONDITION

are different game concepts.

So:

IMMUNITY TO POISON DAMAGE

means no Poison damage.

While:

IMMUNITY TO THE POISONED CONDITION

means the Poisoned condition doesn't affect the creature.

The SRD defines damage-type and condition Immunity separately.

DON'T ASSUME ONE AUTOMATICALLY MEANS THE OTHER

If a stat block lists a creature as immune to a particular Damage Type, use exactly what the stat block says.

If it separately lists Condition Immunities, apply those as written.

Do not silently convert one category into the other.

RESISTANCE, VULNERABILITY, AND IMMUNITY COMPARISON

Rule Effect
Resistance Halve relevant damage, round down
Vulnerability Double relevant damage
Damage Immunity Take no damage of that type
Condition Immunity Condition doesn't affect you

 

DAMAGE TYPES MAKE THESE RULES POSSIBLE

This is why Lesson 25 was necessary.

Consider:

16 FIRE DAMAGE

The amount:

16

tells us how much harm was generated.

The type:

FIRE

allows us to ask:

Does the target have:

  • Resistance to Fire?

  • Vulnerability to Fire?

  • Immunity to Fire?

The Damage Type acts as the mechanical label that determines whether those rules apply.

EXAMPLE — RESISTANT TARGET

Damage:

16 FIRE

Fire Resistance:

Yes.

Final:

8 DAMAGE

EXAMPLE — VULNERABLE TARGET

Damage:

16 FIRE

Fire Vulnerability:

Yes.

Final:

32 DAMAGE

EXAMPLE — IMMUNE TARGET

Damage:

16 FIRE

Fire Immunity:

Yes.

Final:

0 DAMAGE

DAMAGE WITH NO RELEVANT DEFENSE

Damage:

16 FIRE

No relevant Resistance.

No relevant Vulnerability.

No relevant Immunity.

Final:

16 DAMAGE

MULTIPLE DAMAGE TYPES

Some attacks can contain separate damage components.

For example:

PIERCING DAMAGE

plus:

POISON DAMAGE

When a target has a rule applying to one of those types, keep the Damage Types identified so the appropriate rule can be applied to the relevant damage.

EXAMPLE

An attack deals:

8 PIERCING

plus:

6 POISON

The target has:

RESISTANCE TO POISON DAMAGE

The relevant Poison damage is halved:

6 ÷ 2 = 3

The Piercing damage is not modified by Poison Resistance.

So the components become:

8 PIERCING

plus:

3 POISON

Total HP loss:

11

This follows from applying Resistance specifically to damage of the relevant type.

RESISTANCE DOES NOT CHANGE THE DAMAGE TYPE

If:

18 COLD DAMAGE

is halved by Cold Resistance,

the resulting:

9 DAMAGE

is still:

COLD DAMAGE

Resistance changes the:

AMOUNT

not the Damage Type.

VULNERABILITY DOES NOT CHANGE THE DAMAGE TYPE

Similarly:

10 FIRE DAMAGE

with Fire Vulnerability becomes:

20 FIRE DAMAGE

not a new Damage Type.

IMMUNITY DOESN'T CHANGE THE ATTACK INTO A MISS

This is another useful distinction.

Suppose an attack:

HITS

and would deal:

FIRE DAMAGE

but the target is immune to Fire.

The relevant conclusion is:

NO FIRE DAMAGE IS TAKEN

It doesn't retroactively mean that the Attack Roll missed.

The hit and the damage are distinct parts of attack resolution.

Other effects attached to the hit must be resolved according to their own wording.

PRACTICAL DAMAGE DEFENSE FLOW

Whenever damage is dealt, ask:

STEP 1 — WHAT IS THE DAMAGE TYPE?

Fire?

Cold?

Necrotic?

Slashing?

Another type?

STEP 2 — ARE THERE INITIAL ADJUSTMENTS?

Apply applicable:

  • bonuses

  • penalties

  • multipliers

first.

STEP 3 — DOES RESISTANCE APPLY?

If yes:

HALVE

and:

ROUND DOWN

STEP 4 — DOES VULNERABILITY APPLY?

If yes:

DOUBLE

STEP 5 — DOES IMMUNITY APPLY?

If the target has Immunity to that Damage Type:

IT TAKES NO DAMAGE OF THAT TYPE

 

STEP 6 — SUBTRACT THE FINAL DAMAGE FROM HP

After determining the actual amount that gets through:

subtract it from the target's current Hit Points.

COMMON BEGINNER MISTAKES

MISTAKE 1 — THINKING RESISTANCE MEANS NO DAMAGE

Resistance:

HALVES

Damage Immunity:

PREVENTS

the relevant damage.

MISTAKE 2 — FORGETTING TO ROUND DOWN

Resistance is:

HALF, ROUNDED DOWN

 

MISTAKE 3 — STACKING TWO RESISTANCES

Two Resistances applying to the same Damage Type:

COUNT AS ONE

 

MISTAKE 4 — STACKING TWO VULNERABILITIES

Multiple Vulnerabilities affecting the same Damage Type also:

COUNT AS ONE

 

MISTAKE 5 — APPLYING VULNERABILITY BEFORE RESISTANCE

The required order is:

ADJUSTMENTS

then:

RESISTANCE

then:

VULNERABILITY

 

MISTAKE 6 — ASSUMING RESISTANCE AND VULNERABILITY ALWAYS CANCEL PERFECTLY

Because Resistance rounds down, odd damage numbers can produce a different final amount.

The SRD's own example turns:

23

into:

11

then:

22

after Vulnerability.

MISTAKE 7 — CONFUSING DAMAGE IMMUNITY WITH CONDITION IMMUNITY

The SRD distinguishes:

IMMUNITY TO A DAMAGE TYPE

from:

IMMUNITY TO A CONDITION

 

MISTAKE 8 — CONFUSING POISON DAMAGE WITH THE POISONED CONDITION

A creature might interact differently with each because:

DAMAGE TYPES

and:

CONDITIONS

are separate rule categories.

MISTAKE 9 — APPLYING FIRE RESISTANCE TO EVERY DAMAGE TYPE IN AN ATTACK

Resistance applies to the Damage Type named by the rule.

Keep different damage components distinct.

MISTAKE 10 — TURNING AN IMMUNE HIT INTO A MISS

Damage Immunity determines whether damage of that type is taken.

It doesn't itself change the result of the Attack Roll.

LESSON 26 — KEY TAKEAWAYS

RESISTANCE

If you have Resistance to a Damage Type:

HALVE DAMAGE OF THAT TYPE

ROUND DOWN

 

VULNERABILITY

If you have Vulnerability to a Damage Type:

DOUBLE DAMAGE OF THAT TYPE

 

NO STACKING

Multiple Resistances affecting the same type:

COUNT AS ONE

Multiple Vulnerabilities affecting the same type:

COUNT AS ONE

 

DAMAGE MODIFIER ORDER

1. ADJUSTMENTS

2. RESISTANCE

3. VULNERABILITY

 

SRD EXAMPLE

28 FIRE

−5 adjustment:

23

Resistance:

11

Vulnerability:

22 FINAL DAMAGE

 

DAMAGE IMMUNITY

TAKE NO DAMAGE OF THAT TYPE

CONDITION IMMUNITY

THE CONDITION DOESN'T AFFECT YOU

 

NEXT LESSON

LESSON 27 — HEALING, DROPPING TO 0 HIT POINTS, DEATH SAVING THROWS, STABILIZATION, AND TEMPORARY HIT POINTS

You now understand how damage is generated and modified.

Next comes the final and most dangerous part of the Combat section:

WHAT HAPPENS WHEN HIT POINTS REACH ZERO?

In Lesson 27, we will study:

  • Healing

  • maximum Hit Points and excess healing

  • dropping to 0 HP

  • Monster Death

  • Instant Death

  • player characters at 0 HP

  • the Unconscious condition at 0 HP

  • Death Saving Throws

  • successes and failures

  • natural 1s and natural 20s on Death Saves

  • taking damage while at 0 HP

  • Critical Hits and Death Save failures

  • stabilization

  • regaining HP

  • knocking a creature out instead of killing it

  • Temporary Hit Points

  • why Temporary HP are not healing

  • what happens when multiple sources grant Temporary HP

This will complete the entire core Combat section before we begin:

CHARACTER CREATION

with Lesson 28.

SRD 5.2.1 ATTRIBUTION

This work includes material from the System Reference Document 5.2.1 (“SRD 5.2.1”) by Wizards of the Coast LLC, available at https://www.dndbeyond.com/srd. The SRD 5.2.1 is licensed under the Creative Commons Attribution 4.0 International License, available at https://creativecommons.org/licenses/by/4.0/legalcode.