Below is an egg chart for all the Pokemon that can be hatched from eggs in Pokemon Go. Note the % hatch chances here are the chance of hatching that Pokemon given the specific egg distance. Current as of June 6th 2017.
This page is the most useless page on the site. The information here will not help you make any decisions or enhance the way you play. If anything, having this information will only frustrate you when an egg hatches and it is not what you wanted. But, we're human, so perhaps when you have hatched your 4th Poliwag in a row, at least you can calculate exactly how unlucky you are using the information here.
For example. The chance of hatching a Poliwag, given you are walking at 5km egg is 7%. The chance of hatching 4 in a row is 7%^4 = 0.002%
If you like Poke Assistant and the free services it provides, the best thing you can do to give back is to recommend it: