If you use the gov. formula, figure it like this....
your income = a
her income = b
a-b=c
you have pay half of "c"
here is my story from experience.
I have 2 kids from my marriage, we were together 7 years. I made about 55k per year she never worked. when first put on support the based my income vs. hers,(she had none they used minimum wage for 35hrs per week). I had to pay about $245 per week in support only, maintain ins coverage for both, and pay for 75%of everything else. 7mths later found out i was overcharged, because they never noted that i had ins coverage and it was lowered to about $175 per week. Been about 3yrs now I pay a little less. I was married, not sure if you are but that does make it easier. If you 2 are just dating, makes everything alot different. You'll have to basically agree, or goto court to get rights for visitation, and things.
my best advice, get a lawyer, fight for joint custody 50/50!!! then it will even the responsibility of raising the child.