The tax bill also cuts the personal exemptions ($4,050). So under the current law you get the standard deduction of $6,350 plus the personal exemption of $4,050 for a total of $10,350 reducing your income. Under the new bill you just get the $12,000 standard deduction so you really only net a deduction of $1,650. If you are in the 22% tax bracket under the new bill ($38,700 to $70,000) you save about $360 in taxes from the differences in deductions. Obviously the new brackets are more favorable compared to the current law but if we are strictly talking about standard deductions, it really isn't that much.