What is the difference between 'until' and 'up until'?

Solution 1:

Hmm ... Not so sure about 'up' adding nothing.

For me (British English)

"She kept studying until dawn" is clear and straightforward.

"She kept studying right until dawn" is not clear, or idiomatic.

"She kept studying up until dawn" is also clear but doesn't really add anything to the first version (here the up is redundant).

If I want to emphasise just how very close to the dawn she continued to study I would say "She kept studying right up until dawn"

This is a common usage in my experience. Consider another example:

Put the cupboard against the wall.

Put the cupboard right up against the wall.

I think, for me, (right) up means something like '...to the point/position where it is precisely...'

Solution 2:

The "up" in "X up until Y" means that X was so or was happening immediately before the event or condition described in Y. Without "up", it wouldn't necessarily be immediately.

Solution 3:

I think it is a subtlety of emphasis of interest, based on my personal experience and agreement with at least one official dictionary.

According to the Collins English Dictionary, "until" means something happens during a period of time before another event and then stops after that event. It is uninteresting exactly when the first thing stopped, only that it stopped before the second.

Again, according to the Collins English Dictionary, "up until" or "up to" points to the latest time at which a thing may occur or the last moment of the period of time to which you are referring. It is interesting that the first event continued exactly to the moment the second began.

"She stayed awake until he came home." - She undoubtably did not instantly fall asleep when he walked in the door, but that doesn't concern us. We care that she didn't start getting ready for bed before he came home.

"During this class you will take the test and we will review it. You have up until 15 minutes before the end of class to work on the test. Then you must stop, and we will review it." - We care about the exact minute that you stop studying.

For what it is or isn't worth, I am a native speaker of U.S. American English, originally from California, and this is the way I use these terms.