Does a countered spell cost a spell slot?

Question

When a spell caster is interrupted by a counterspell, does the countered spell use a spell slot? The spell description reads, in part:

You attempt to interrupt a creature in the process of casting a spell. [...] On a success, the creature's spell fails and has no effect.

In a related case, spells with longer casting times "[fail, but] don't expend a spell slot" specifically when the caster doesn't use an action to concentrate on the casting, or when concentration is broken as when maintaining a spell (PHB 202).

Should the same outcome be assumed for spells that are countered?

What about spells with shorter casting times?

Answer 1

Depends if the countered spell required a slot to cast

No, if the spell did not take a slot to cast

Some classes, such as Warlocks and Monks, can attempt to cast spells without using spell slots. But counterspell still has the potential to stop those spells. Also, counterspell could counter a spell cast as a ritual, in which case, again there are no spell slots involved.

For those reasons you won't find any reference to spell slots in the counterspell text.

Yes, if the countered spell required a slot to cast

If a caster does rely on spell slots to cast a spell, and their spell is countered by counterspell, then yes the slot is expended. That is my interpretation based on the following.

When a character casts a spell, he or she expends a slot of that spell's level or higher, effectively "filling" the slot with the spell. (PHB p.201)

The spell is still cast and the slot is filled whether the spell has an effect, or "has no effect." It is the casting of the spell, not the outcome of the spell, that causes the slot to be used.

The word "interrupted" has no effect on the interpretation. When you make an opportunity attack on a creature leaving your reach, the same language is used. Your OA "interrupt[s] the provoking creature's movement" but it does not end the movement. Likewise, counterspell does not end the casting of the spell. It only negates its effects.

I found a few more references to support my interpretation:

1. Magical Wards

   Spells cast within the slave pen have no effect, and any slot or magic item charge expended to cast such a spell is consumed (Out of the Abyss p.15 )

2. Antimagic field

   ...A slot expended to cast a suppressed spell is consumed (PHB p. 213)

These are just two examples of magic causing the casting of spells to fail or have "no effect" just as described in the counterspell text.

Answer 2

Yes.

The countered spell uses whatever slot it would have, had it had not been neutralized by counterspell.

Spells with long casting times

The general case above still holds for spells with a long casting time. The targeted caster retains the spell slot if they don't spend their action casting or if they have their concentration broken. Counterspell causes neither of these conditions, so the slot is lost as usual.

Spells with short casting times

Counterspell is cast as a reaction with the criterion "you see a creature within 60 feet of you casting a spell". Nothing prevents countering spells with short casting times as long as the caster is visible. A sorcerer's Subtle Spell metamagic ability could conceal the casting, however.

Answer 3

Yes

If a successful casting of the spell would have consumed a spell slot, then countering the casting of the spell causes that slot to be spent. To see an excellent explanation of how you can come to this conclusion through the written rules, see Lumenbeing's answer to this question.

We have also been given unofficial developer guidance on this issue. Jeremy Crawford, lead rules designer, has given an answer that heavily implies that this also applies to spells with longer casting times.

Question: A interrupts with Counterspell an ongoing spellcasting process of B (requires longer casting time), B losts [sic] his spell slot?

Jeremy Crawford: A successful counterspell causes a spell to fail, regardless of that spell's casting time. The thwarted spell's slot, if any, is spent.

The "if any" part of his answer would indicate that a countered spell would not consume a spell slot if that spell did not require a slot to successfully cast (e.g. it was a ritual). But if the spell requires a spell slot to cast, Crawford's answer indicates that the slot is then lost.

Answer 4

The general consensus would be YES, and it is true, but only to spell with a casting time as fast or faster than a reaction or that are already been cast (if counterspell apply to those, that the theory suggest that, in fact, it affect those). Any other spell their slots are not consumed, this is because:

You attempt to interrupt a creature in the process of casting a spell... On success, the creature's spell fails and has no effect.

And we have the casting rules on longer spells in PHB 202 for "longer spells".

Certain spells (including spells cast as rituals) require more time to cast: minutes or even hours. ... If your concentration is broken, the spell fails, but you don’t expend a spell slot.

And also we have this question that shows that you can counterspell a counterspell.

How a counterspell can counter a spell as fast as itself? If we consider the casting speed of counterspell as a factor, we can safely assume that a counterspell not only interrupt the casting process, but also disturb the weaver/magic of the spell at the moment of casting it.

Now, in order to determine if a spell slot is used we have this extract from the PHB (201) and the consideration of the "longer spells" rule. This seems contradictory, but we can think of a casting time as the preparation of the weaver/magic before exerting the force to the weaver/magic to cast the spell. It is logical to think that the taxation and spell slot is consumed at the moment of releasing and pushing the magic, and this can be applied to any spell with a casting speed longer than counterspell. Therefore, any spell with a casting time slower than the counterspell, this is any non-reaction spell, are not consumed and the slot not used.

Regardless of how many spells a caster knows or prepares, he or she can cast only a limited number of spells before resting. Manipulating the fabric of magic and channeling its energy into even a simple spell is physically and mentally taxing