I'll start off by saying I really hope this makes sense (it does in my head, but sometimes it gets lost in translation

)
I left my Kindle at home today

and of course today is such a slow day at work, I wanted to finish up a book I was reading. I downloaded the book into my iPhone, but I was curious if they sync up. For example, if I read 3 chapters on the iPhone, when I get home do I have to jump ahead in my Kindle or will it know where I left off.
I thought somewhere I read that they do sync up, but I can't find anything about that - so I could just be losing it.
If anyone knows please let me know.
Thanks!!
Kat