[RPG] Do I add damage bonuses when casting a spell from a magic weapon


In 5e, if a spell is only learned as a part of having a weapon with the ability to cast it, because it is technically an attack with the weapon and not me directly casting the spell, would I add the damage bonus to the damage roll?

I have a great axe that allows me to cast call lightning 3 times per long rest. It's a homebrew version of Stormbreaker from The Avengers. My DM and I just aren't sure if we should add the bonus to the damage for the spell being cast from the weapon itself. We are just wondering if there are any official items with similar abilities, and how they would work.

By damage bonus, I mean the relevant modifier you add to damage rolls for attacks with the weapon.

Best Answer

You don't add your weapon damage bonus to spells it grants you.

Since it's a homebrew item, its function is up to your DM.

However, the only relevant damage bonus to either greataxes or call lightning are the Strength modifier to damage, and any magic weapon bonus.

  • As per Player's Handbook p.14, under "Weapons", Strength modifier to attack and damage only applies for attacks with melee weapons, not spells cast using melee weapons.
  • As per Dungeon Master's Guide, p.213, a weapon's magic bonus only applies to attack and damage rolls made with the weapon, not to damage rolls made with spells that you gain the ability to cast while you hold the weapon. The Sword of Kas, DMG p.226, is a +3 sword which grants the ability to cast call lightning, and it specifically phrases it that you don't cast that spell with or from the weapon, but rather that you gain the ability to cast that spell while you have the sword. If your DM wishes to follow this item as precedent, then you specifically don't add the weapon's enhancement modifier to spell damage.

If the weapon instead dealt additional lightning damage on a successful melee hit, then you would still add your Strength modifier as normal.