From my understanding, it will take some time for the IRS to implement the new changes to the system, including deductions. I read (before the the approval) that many Americans are getting taxes filed ASAP if the old system generates more in return. Just the opposite applies if you can take more under the new tax structure. I am not an accountant but the new tax bill will go into effect during the filing time period, just when is not known. I have my taxes prepared and for the last 10 years, I pay an estimate tax to the IRS on the last day, and file an extension.