Hi, So I entered my girlfriend about 2.5 inches in and then exited. Not one of us uses any form of protection. What is the chances that precum occurred and if it did what is the chances of her falling pregnant?

Yes, there's a chance no matter how slim.

Falling pregnant potential dad?

The time to worry about this is when you say no to birth control.

It can happen, but not the most efficient way to become pregnant. Best to not take any chances, or at least lower the odds, and figure out the best birth control options for the two of you or refrain from getting that intimate.

There is no way to say 10 percent, or 20 percent, factors of her ovulation, and then just an issue of how much sperm determines many factors.

But yes there is a chance,

No matter what the odds are... it WILL happen to someone. In this case... many, many, people. What would make you think how far has anything to do with it? Seriously?