But, there are really two options. One is when you are speaking and one when you are writing.
Speaking usually is less formal, and you can use "depends on."
Writing is more formal, and you have to use "depends upon"
When are you going to go to China? Well, it depends on the price quote I can get from the factory.
Where are you going on vacation next year? It depends on the weather, we might go to Thailand or to Bali.
Which car you purchase depends upon which state you live in.
The lawyer depends upon his paralegal to do most of the research about the case.
I hope that this post makes it a bit clearer for you with these two phrases.
Rachael Alice Orbach - Professional English teacher.