it's not a credit it's a deduction - credit saves you $ for $ deduction saves a max of about 40% federal there is also a 4th category, for partherships, and the like partners may deduct certain expenses against the partnership results , these to would need to be subtracted in fiquiring QBI.
also say there are 3 trades or businesss 1 and 2 - $20,000 profit each 3 - $10,000 loss the loss must be allocated to the profitable ones so each of 1 and 2 would only show a $15,00o of QBI and it gets even more complicated if any are a specified service trade or business.
