State tax withholding calculation

I am trying to calculate the taxes myself from my Gross income based on my biweekly paycheck. I have figured out the federal. The only one I am having trouble with is the state tax. I cannot figure this out for the life of me. I am hourly with overtime so my pay is different each week. New York State by the way. So federal tax withholding was gross minus 401k and benefit deductions all multiplied by 26. Then subtracted by standard deductions. Then just using the marginal tax bracket to figure out how much to take out. Why is am I not getting the same for state. Is there something I’m not factoring in for the state? Thank you guys.