What is the purpose of a spell attack modifier?

Question

In the 5e Player's Handbook, the Wizard Class on page 114 defines a spell attack modifier, but the spells I have looked at all specify attack damage without using this modifier or mentioning it. I can't determine what it has to do with anything. Where does it come into the game?

Answer 1

There are two ways that most damage spells work in 5e. You've obviously already found the spell attack modifier calculation. But you're probably looking at a spell wondering how to apply it.

The first is the following form from Fireball:

....Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity Saving throw. A target takes 8d6 fire damage on a failed save, or half as much damage on a successful one.... (PHB 241-242)

This is a spell with a saving throw. The target(s) need to make a Spell Save DC specified by the casting class that the spell belongs to (so if you're a wizard, you use INT, if you're a Sorcerer you use CHA).

For the second, we'll use the example from Fire Bolt:

Make a ranged spell attack against the target. On a hit, the target takes 1d10 fire damage.... (PHB 242)

This is the other common damage spell type. In this case you (as the attacker) roll your d20 and add your spell attack modifier.

Occasionally you'll find a spell that does damage without an attack or save, these spells just simply do their damage.

So if you're trying to figure out whether you damage someone with a damage spell, look for the following:

• Target makes a saving throw (in this case, they use their ability and add it to their d20 roll, and the target number is your spell save DC)
• You make a spell attack (in this case you are rolling your d20, adding your spell attack modifier and comparing it to their AC)
• Damage is simply applied without an attack or save (See Magic Missile).

Answer 2

From D&D Player's Basic Rules v0.2, p30

Spellcasting Ability

Intelligence is your spellcasting ability for your wizard spells, since you learn your spells through dedicated study and memorization. You use your Intelligence whenever a spell refers to your spellcasting ability. In addition, you use your Intelligence modifier when setting the saving throw DC for a wizard spell you cast and when making an attack roll with one.

Spell save DC = 8 + your proficiency bonus + your Intelligence modifier

Spell attack modifier = your proficiency bonus + your Intelligence modifier

The attack modifier is used when making your attack roll. This is the roll to determine if your (spell) attack hits.

The process is the same as for other forms of attack:

• Roll d20, add your attack modifier
• If the result is equal or higher than the target's AC (Armour Class), then you have hit.
• If you hit, you roll for damage. If you miss... you don't.

(Note, some spells do not require an attack roll. Refer to the individual spell descriptions.)

Answer 3

Spell attacks don't allow saving throws

A spell attack basically decides if the spell attack hits the target. It's different from spell saving throws in that it depends less on the target's ability to dodge, and more on how well your character can aim.

It can apply to ranged spells or melee spells, as long as you use a spell attack.

Examples of melee and ranged spell attacks

Melee Spell Attack

Shocking Grasp (Range: Touch) Make a melee spell attack against the target. You have advantage on the attack roll if the target is wearing armor made of metal. On a hit, the target takes 1d8 lightning damage, and it can’t take reactions until the start of its next turn.

Ranged Spell Attack

Fire Bolt (Range: 120 feet)

Make a ranged spell attack against the target. On a hit, the target takes 1d10 fire damage. A flammable object hit by this spell ignites if it isn’t being worn or carried.

Compare with spell that forces a saving throw

Poison Spray (Range: 10 feet)

You extend your hand toward a creature you can see within range and project a puff of noxious gas from your palm. The creature must succeed on a Constitution saving throw or take 1d12 poison damage.

The effectiveness of the spell on your enemy is tied to your spell casting ability, which for a wizard would be Intelligence, while the effectiveness of your spells that call for a save are based on your DC (tied to your spell casting ability) AND the ability of your target (and thus it's chances for save against your spell DC).

Spell attack modifier = your proficiency bonus + your Intelligence modifier

Spell save DC = 8 + your proficiency bonus + your Intelligence modifier (Basic Rules, p. 30).

The spell save DC is then opposed by your opponent's ability score that it tied to the spell. Your target rolls, not your, and then tries to 'hit' the saving throw score based on your DC. (In the above example, the target with a low Constitution is less likely to save than one with a high constitution).

Answer 4

I wanted to provide an example of a spell that uses Spell Ability as a damage modifier based on the question. One example is the Druid spell description for Shillelagh (PHB p.275), which says "...you can use your spellcasting ability instead of Strength for the attack and damage rolls of melee attacks using that weapon, and the weapon's damage die becomes d8." Shillelagh is a transmutation and is cast on an object, not on another creature, so it is a good example to show a difference between Spell Ability as a damage modifier and why Spell Attack modifier is not used.

The PHB on p.66 under Spellcasting Ability (for Druids) says "You use your Wisdom whenever a spell refers to your spellcasting ability". Thus, a wisdom of 18 would give a +4 for ability. (Wizards would use Intelligence instead but the description is the same for all casting classes).

So back to the example: If a Druid with a Wisdom of 18 (+4), Strength of 10 (0) and proficiency of +2 were attacking with a normal quarterstaff one-handed, the attack would be +2 and 1d6+0 damage. After casting Shillelagh, the weapon would be +6 to hit (from +2 weapon proficiency and +4 Spell Ability instead of strength), 1d8+4 damage (modified by the +4 Spell Ability).