How long can a readied spell be held before it's lost?

Question

From RAW, it's clear that a character can ready a spell that has a casting time of 1 action and release the spell when the trigger occurs or directly after the trigger finishes¹: Provided, that the character's concentration is not broken.²

Is there any time limit (rounds, turns, etc.) on how long a character can hold a readied spell, as long as concentration is maintained?

Example 1: How long can I wait just around the corner with a readied lightning bolt having a trigger of "I release the spell when a creature (or anything) comes around the corner"?

Example 2: How long can a back row spellcaster hold a readied dimension door with a trigger of "If an enemy breaks through the front line, then I release the spell"? Which would allow the spellcaster to move and attack with a ranged weapon each turn with an escape plan. ("Normal activity, such as moving and attacking, doesn't interfere with concentration." PBR, p. 80; PHB, p. 203)

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1. Under "Adjudicating Reaction Time" in the Dungeon Master's Guide:

   Use this rule of thumb: follow whatever timing is specified in the reaction's description. For example, the opportunity attack and the shield spell are clear about the fact that they can interrupt their triggers. If a reaction has no timing specified, or the timing is unclear, the reaction occurs after its trigger finishes, as in the Ready action. [Emphasis added] (DMG, p. 252)

2. According to the Player's Basic Rules and Player's Handbook:

   When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell's magic requires concentration. If your concentration is broken, the spell dissipates without taking effect. For example, if you are concentrating on the web spell and ready magic missile, your web spell ends, and if you take damage before you release magic missile with your reaction, your concentration might be broken. [Emphasis added] (PBR, p. 72; PHB, p. 193)

Answer 1

The recently released Player's Handbook Errata clarifies this:

Ready (p. 193). You have until the start of your next turn to use a readied action.

Answer 2

Before the start of your next turn.

The Ready action specifies in its description that you can only hold your action until the start of your next turn. (PHB, p. 193)

The notes about concentration and the breaking thereof are additional to this limit, not a replacement thereof — it specifies that the normal Ready-Reaction timing stays the same when it says

you cast [the spell] as normal but hold its energy, which you release with your reaction when the trigger occurs.

There are no other notes about Readying spells being different than Readying any other action, so they get no special treatment and expire like any other Readied action.

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This is ripe for house ruling though. I imagine it will be a relatively common house rule, either on purpose or by accident of not noticing the limit in the first place.

It would have a significant impact on party tactics though (as your dimension door example demonstrates), and will likely be polarising between different groups or between players used to one way joining groups with DMs used to running it the other way.

Answer 3

p 192 of the PH say

When you take your action on your turn, you can take one of the actions presented here ...

p 193 says

When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell’s magic requires concentration (explained in chapter 10).

So, you take ready (a spell), the trigger does not occur and your turn rolls around again. So, what can you do?

As written, the "energy" is not released so to my mind I can see several options:

1. Its gone - too bad
2. You could take Ready again with the same trigger
3. ... or a different trigger; possibly including the trigger "Now!" (equivalent to 4.)
4. You could take the "Cast a Spell" action to release the energy
5. You could take any other action and so long as you maintain concentration the spell is sitting like a malignant toad in your brain ready to be used on some future action ("Cast a Spell" or "Ready").

Personally, I would rule any or all of 2-5 as No 1 would pretty seriously discourage the use of Ready to cast a spell and none of the others seem overpowered - essentially you have given up an action and a spell slot and concentration for some nebulous future benefit. Contrast this with Ready vis a vis any other action which only makes you give up your action.

The advantage of this is it is readily applicable in a non-combat situation, the same mechanics are in play, just implicitly rather than explicitly, so you can hold the spell until you use it or your concentration breaks (voluntarily or involuntarily); effectively taking Ready round after (implicit) round.

Answer 4

Sage Advice Compendium: only until the start of your next turn

How to rule this has been clarified in the Sage Advice Compendium. Here is the entry (Version 2.7):

How does readying a spell work? Do you lose your spell slot if the trigger never occurs? A readied spell’s slot is lost if you don’t release the spell with your reaction before the start of your next turn.

This ruling confirms the conclusion given in Dyndrilliac's answer.

Answer 5

The Errata on this section has changed (as of the 2018 errata) and as a result readied spells can be held for as long as desired.

The errata now reads:

Ready (p. 193). The second sentence now reads, “To do so, you can take the Ready action on your turn, which lets you act using your reaction before the start of your next turn.”

This wording no longer precludes holding a readied spell for as long as you like, as the Ready action no longer mandates that it must be used by the start of your next turn. Instead the Ready action now enables you to act using your reaction before the start of your next turn.

The specific rule for holding spells is detailed later in the Ready section:

When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell's magic requires concentration (explained in chapter 10).

So holding onto the spell now only requires concentration. Actually releasing the readied spell, requires a reaction. This reaction can be re-enabled by future use of the Ready action.

Answer 6

The spell slot is consumed as you ready the spell. According to the official rules, you can only maintain concentration until the start of your next turn (see Sage Advice).

That said, it's probably a common house rule (which probably includes Jeremy Crawford's table) that you can maintain concentration for more than six seconds.

Personally, I'd allow it to be held indefinitely. After a considerable amount of time (e.g. during a short rest), I'd call for one or two constitution saving throws with DC 10, depending on the environment. Of course, if the character were to sleep (as in during a long rest), the character would become unconscious, and thus incapacitated, which would break concentration. If that character didn't need to sleep (i.e. the Elf's trance trait), then I'd also say that the concentration was broken during the trance.

I would allow characters to change the trigger as an action on their turn (effectively, taking the ready action again). The characters could also release the energy as an action on their subsequent turns.