Naturally if you got it in say, your eye, then the odds are pretty low, but Ill assume that you understand the basics.
I'd say around 37.35%, however without further information, I cannot be any more specific. It's a possibility. Get a pregnancy testing kit.
However if it has just happened, have a shower. Then get a pregnancy testing kit. You will have to wait 2 weeks before the test will be accurate to take, and sufficient levels of human chorionic gonadotrophin are detectable in the urine.
Follow the instructions on the packet. If its positive, the chances for you of getting pregnant from pre-cum is 100%.
Use a condom a little earlier next time however if you actually want a baby, you'll probably need to go a little further in the future.