Many chapters cease and desist at the natural ending of a scene, but more often than not, a chapter can end right in the middle of the action—or even in the middle of a conversation. Just like there's no rule for chapter length, there's not a rule for where to end one.
So what do you do?
Here's my take. End on strong note that you’ve been building up to for the whole chapter. That note could be a realization or revelation. It could be ending one plot point and signaling another. It could be a cliffhanger. It could be a quiet moment or a call to action.
And that note has to propel the reader into the next chapter.
For instance, here’s a chapter ending from Scott Westerfeld’s Behemoth:
“Look smart, gentleman,” Dr. Barlow said. “We have an elephant to catch.” (102)
This one just sounds great—and you’re looking forward to what happens next. Here’s another:
Alek looked up and saw it…
A gyrothopter hovering directly overhead. (348)
Both chapters break in the middle of the action, but the end signals a change in direction. For instance, in the last example, Alek and the others have been trying to sneak around Istanbul, but now they’ve been discovered. Then next chapter will be about engaging the enemy instead escaping.
In Levianthan and Behemoth, Westerfeld keeps the story going at a very brisk pace, but chapter endings don't need to be so plot-oriented. The end note of a chapter can be thought-provoking and quiet, or whatever you need it to be. It just has to keep the overall tension of the story moving forward. The reader must want to turn the page to find out what happens next.
My last bit of advice. Don't bury your end note with a lot of stage direction. You can save the "and then they caught the train to Barcelona" stuff for the beginning of the next chapter--or let it fall between the chapter cracks. End on a strong note and get the hell out.
What makes a chapter satisfying for you?