Taxes are a moving target because many dollar limits and percentages change annually due to increases in inflation. However, some limits and amounts are fixed in the Tax Code and cannot be changed without an act of Congress. Still others are set by the IRS for administrative convenience and are not adjusted annually but could change at the IRS's whim. To help you plan ahead and to figure estimated taxes for 2018, where necessary, lists of items that may or may not change for the next tax year follow. The adjustments for 2018 are listed in the Supplement to the extent that these were available by February 2018.