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In D&D 5e, many spells have a fixed duration measured in common units of time - minutes, hours, days and so on. Does the caster of a spell have any special insight as to when a spell they cast will end, and if so, is this knowledge vague ("about half", "very nearly gone") or precise ("in five, four, three, two...")?

This question concerns all spells with a duration, regardless of whether they require concentration. Whether a caster is aware that a spell has ended, other than due to its duration having expired, is outside the scope of the question.

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    \$\begingroup\$ I would also be curious as to whether a caster can determine roughly when a spell they did not cast will end, but that may be a separate question. \$\endgroup\$
    – sptrashcan
    May 31, 2019 at 6:14
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    \$\begingroup\$ @Akixkisu: I'd say it's definitely related, but not a duplicate, since not all spells with non-instantaneous durations require concentration. (That question is also under the misconception that their spell ending through other means entails the loss of concentration, which is also a separate issue.) \$\endgroup\$
    – V2Blast
    May 31, 2019 at 9:23
  • \$\begingroup\$ Again, not all spells with non-instantaneous durations require concentration. Some last for minutes or even hours without requiring concentration (e.g. Disguise Self or Mage Armor). Because the questions are different (this one is broader than the other one), they are not duplicates as currently written, even if they are related. \$\endgroup\$
    – V2Blast
    May 31, 2019 at 9:29
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2 Answers 2

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They probably don't get any special knowledge

But the caster does have the knowledge of how long the spell lasts and when it was cast. Depending on how the spell was cast and who was present, the spell’s duration may in fact be only known to the caster.

Two possibilities that may allow a caster to keep track of the time left in a spell.

  1. The Keen Mind feat (PHB, p. 167) states:

    You have a mind that can track time, direction, and detail with uncanny precision. You gain the following benefits.

    • Increase your Intelligence score by 1, to a maximum of 20.
    • You always know which way is north.
    • You always know the number of hours left before the next sunrise or sunset.
    • You can accurately recall anything you have seen or heard within the past month.

    Being able to track time with uncanny precision would likely allow for the caster to know the duration the majority of the time.

  2. A pocket watch

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  • \$\begingroup\$ As a side note, the existence of pocket watches - or indeed any highly reliable measure of time - has significant implications for ocean navigation. \$\endgroup\$
    – sptrashcan
    Jun 3, 2019 at 15:28
  • \$\begingroup\$ True, especially outside of gnomish lands, the rock gnome can create a “Clockwork Toy” lending to the possibility of pocket watches. \$\endgroup\$
    – Alk
    Jun 3, 2019 at 18:14
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There are no rules that I am aware of

So; whatever works best at your table.

At my tables I like to give my players all the information that could benefit them. I tell them lore without knowledge rolls, and I tell them how long spells have left as long as they have seen the casting (i.e. You can't walk into an area of silence and know there are only 10s left).

This works well and gives the players the information they need to plan. Everyone I have DMed for appreciates this level of knowledge, and frankly they are playing extraordinary characters who in some cases have dedicated their lives to things like casting spells and tracking how long they last so I don't find it a stretch.

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    \$\begingroup\$ It might be worth noting that a caster that has a spell cast and leaves wouldn't know if someone came along and dispelled it either. So other than counting or keeping time in some way... \$\endgroup\$
    – Slagmoth
    May 31, 2019 at 12:03
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    \$\begingroup\$ This answer is more popular and contains what is probably the more practical advice for running the game. I am accepting the other answer because it addresses the question directly in more detail. \$\endgroup\$
    – sptrashcan
    Jun 3, 2019 at 15:21

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