The Rule (As Written) Explained
According to 5e rules, casting a spell with a casting time of 1 Bonus Action is subject to a special rule. This rule says that if you cast a bonus action spell:
- You cannot have used another bonus action already in the same turn.
- If you cast another spell in that same turn, it must be a cantrip with a casting time of 1 Action. You cannot use leveled spells, Reaction spells, Quickened spells, etc.
Why This Needs a House Rule
This rule is somewhat notorious in online D&D discussions for a couple of reasons. One is that it’s hard to remember. It doesn’t come up super often since Bonus Action spells are fairly uncommon outside of a handful (like Misty Step and Shillelagh), and most of its interactions come up during complex and tense moments in combat when a player is trying to accomplish a specific sequence. It’s frequently difficult to remember when this rule applies if there is any delay between the bonus action cast and a later spell selection, or if the spells are cast in reverse order (a leveled action spell followed by a bonus action spell).
It’s also very confusingly worded in the PHB, and takes quite a bit of unpacking to understand what the series of conditions and exceptions means. And even when it’s understood, it’s not always immediately clear what the intention of the rule is in terms of what it’s trying to accomplish or prevent.
The re-worded explanation above hopefully does a slightly better job of making the rule itself more clear, but the intention bit is worth examining because it will help explain why this house rule is actually a change to a couple of other rules and the elimination of this rule altogether.
Why Does This Rule Exist?
The Bonus Action spellcasting rule exists, as near as I can tell, primarily to avoid certain builds from becoming better than a vanilla Wizard when it comes to casting leveled spells. In particular, Sorcerers’ Quickened Spell metamagic allows casters to reduce the casting time of spells from 1 Action to 1 Bonus Action. Without the Bonus Action rule, Sorcerers with those features could in theory cast two Fireball spells in a single turn, which, in terms of the action economy, would be better than a single Wizard could accomplish.
It’s worth pointing out that this rule doesn’t really accomplish the game balance effect it is meant to entirely. Clever build optimizers will note that any spellcaster who dips into the Fighter class for a couple of levels will get Action Surge, which gives a character an extra action once per Rest. It’s not quite as efficient as Quickened Spell since, using the example of Fireball, by the time a Sorcerer has access to that spell at 5th level they can already use Quickened Spell twice before needing a Long Rest (to recover their Sorcery points and the 3rd-level spell slots). But it does give the Wizard class the ability to castFireball twice in the same turn as early as 7th level, albeit only once per Short Rest. The point being, preventing characters from casting multiple leveled spells in the same turn is not the intention of the Bonus Action spellcasting rule, or if it is, it doesn’t work.
There is also one other small effect the rule has, which is to prevent characters with access to multiple bonus actions and spellcasting from using multiple bonus action spells, although the way it does so is awkward. I believe this effect falls under the same umbrella as using Action Surge to cast more than one action spell and is part of the balance issues.
The House Rule(S)
This house rule comes down to three components. The first two are modifications to a couple of specific features the RAW is meant to address as a blanket. By house ruling the features, we can accomplish the game balance effects where they matter and then, with the third component, remove the clunky blanket rule, to open up interactions that are otherwise affected in the rules as written but don’t actually have negative impacts to game balance. However, there is one aspect to the blanket rule that I think needs to be there for balance, but we can simplify the rule to avoid multiple Bonus Action casting time spells per turn.
Note that the feature updates are mostly pulled over verbatim from the One D&D playtest rules, and the key modified portions from the original SRD rules are italicized for clarity.
Quickened Spell
When you cast a spell that has a casting time of 1 Action, you can spend 2 Sorcery Points to change the casting time to 1 Bonus Action for this casting. You can’t modify a spell in this way if you’ve already cast a spell of 1st level or higher on the current turn, nor can you cast a spell of 1st level or higher on this turn after modifying a spell in this way.
Action Surge
You can push yourself beyond your normal limits for a moment. On your turn, you can take one additional action, except the Cast a Spell action.
Once you use this feature, you must finish a Short Rest or Long Rest before you can use it again. Starting at level 17, you can use it twice before a Rest, but only once on a turn.
Bonus Action Spellcasting
You may only ever cast one spell with a casting time of 1 Bonus Action per turn. This applies at the time of casting and ignores casting time from the spell’s description (if different).
It is worth noting that any shenanigans which are not covered by this rule but are meant to enable multiple castings of leveled spells with the same casting times by the same spellcaster in the same turn will be adjudicated as invalid. We don’t actually want casters flinging multiple fireballs in a turn or trying to give Sanctuary to half the party, but Misty Step, Fireball, Counterspell as Bonus Action, Action, Reaction should be perfectly valid.
HR06, Active, v1.1.1