Honestly I define Fate and Destiny a little differently than some might.
To me, Fate is made up of all the inevitable events that you cannot, or can no longer change the course of, or prevent from happening to you. Of course Fate is controlled by Destiny.
Destiny is where you're headed in life. It consists of all the things you can freely influence, as well as the factors that are not so easily influenced, but are possible if you play your cards right. You dictate your Destiny by how you act, react and live. Of course, Destiny only changes to Fate at the last possible moment when it's impossible for you to take a different path and change things.
Additionally, Fate can be used in the past tense. It's the best term to describe what has happened to a person when addressing Fate/Destiny in my opinion.
With all of that being said, I believe in both of them, but very very little of your Fate is predetermined before birth. Just the general stuff like, you will die, you will get old, ect...
Where natural laws and irreversible natural process take effect mainly