Do effects with the duration of one minute end at the beginning or the end of your turn?

Question

The Rage class feature of the Barbarian allows you to rage for one minute given you either took damage or attacked every round.

A round is defined as a 6-second interval. So the rage can last up to 10 rounds. Now my question is, does it end at the end of your 10th round or at the beginning of your 11th round?

There are other effects like that, also concentration spells with the duration of 1 or 10 minutes. Sometimes those are activated before combat starts and end during combat.

In general:

Does an effect/concentration end at the end of your last turn during the timespan or at the beginning of your first turn after the timespan?

Answer 1

All effects with a fixed duration measurable in rounds end just before the beginning of one of your turns. (Otherwise, their duration would be too short to be a full round, or a full 2 rounds, etc.)

We can see this by looking at a duration of 1 round, and applying the same logic to the case of 10 rounds.

A duration of 1 round, measured in turns, is “each participant in a battle takes a turn” (PHB, p. 189) — or put another way, one turn each for you and everyone else. Since you enjoy the benefits of an effect like Rage on the turn you activate it, that's one turn of effect for you; everyone afterward also “enjoys” the effect for their turn after you, until the end of the turn of the creature just before your next turn. When your next turn begins, you would be enjoying the effect for a second turn, therefore the 2nd round of the effect begins as your 2nd turn begins.

Thus the dividing line between the rounds, for an effect you enjoy on its first turn of activation, is just as/before one of your turns begins.

(There are a few exceptions, but these explicitly say when they end in relation to your turn. Most are single-round spells that alter your next action, which explicitly extend to the end of you next round so that they're not useless — you can think of effects like that as beginning to be “enjoyed” by you and everyone else only after the end of your 1st turn.)

Now we can extend this out to 10 turns, to see that Rage ends just before your 11th turn begins. For simplicity, we'll call the turn an effect starts “your 1st turn”, no matter how long combat has been.

• A duration of 1 round begins on your 1st turn and ends just before the beginning of your 2nd (next) turn. Otherwise, it would not be a full round long.

• A duration of 2 rounds begins on your 1st turn and ends just before the beginning of your 3rd turn. Otherwise, it would not be a full 2 rounds long.

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• A duration of 10 rounds begins on your 1st turn and ends just before the beginning of your 11th turn. Otherwise, it would not be a full 10 rounds long.

So in the case of rage, it ends just before you take your 11th turn, preventing you from enjoying 11 rounds of rage but allowing you to enjoy the full 10th round of your rage, including during everyone else's turns.

Answer 2

I would argue that the effects last an exact number of rounds, just as they say they do.

If you activated it during your turn, logically it must expire during your turn.

Since the placement of actions within your turn is inexact, I argue that the player can decide which actions occur before/after the effect expires, just as they can decide which actions occur before/after the effect is activated initially.

Some examples:

A Wizard casts True Strike, then on their next turn they Ready an Attack for when their enemy enters their reach. However, the True Strike effect must end on their turn, and therefore does not benefit the Attack.

A Multiclass Barbarian/Warlock enters Rage, then 10 rounds later they can Attack whilst the Rage is still active, then Misty Step away after the Rage ends (because they cannot cast spells whilst Raging).

A Cleric casts Bless on themself, then 10 rounds later they enter the space affected by a Create Bonfire spell and end their turn in that space. They can choose to enter the space before the Bless effect expires, adding the +1d4 bonus to their Saving Throw. However, at the end of their turn they must make another Saving Throw because they are still standing in the bonfire, but since this occurs at the end of their turn the Bless effect has unambiguously expired by this time and they no longer get to add the bonus.