要するに means "in short", "basically": it boils down what has just been said to its main point. It opens the sentence that gives the summary, and the sentence often ends in or, as a question, .
、きごう？
Basically, you don't have enough money, right?
、きごう？
That was a long explanation, but in short, does that mean you agree?
、。
His story was complicated, but in short, he wants to change jobs.
要するに or つまり
restates something in other words, or draws the conclusion that follows from it: "that is", "which means". 要するに cuts the detail away and keeps only the core.
、。
He is my mother's older brother, that is, my uncle.
、。
You said a lot of things, but in short, you're against it, right?
The first sentence has nothing to sum up, so 要するに does not fit there.
- × 母の兄、要するに私のおじです → 母の兄、つまり私のおじです
Summing up someone else
Used on what someone else has just said, 要するに can sound as if you are brushing their details aside. Turning it into a question with ということですか makes it a check rather than a verdict.
、。
So basically, are you saying we won't make the deadline?
Lingaku