A deduction is allowed for the expenses paid during the tax year for the medical care of the taxpayer, the taxpayer's spouse, and the taxpayer's dependents to the extent the expenses exceed a threshold amount. To be deductible, the expenses may not be reimbursed by insurance or otherwise. If the medical expenses are reimbursed, then they must be reduced by the reimbursement before the threshold is applied. Under pre-Act law, the threshold was generally 10% of AGI.

And, under pre-Act law, for alternative minimum tax (AMT) purposes, the medical expenses deduction rules were modified such that medical expenses were only deductible to the extent they exceeded 10% of AGI.

New law. For tax years beginning after Dec. 31, 2016 and ending before Jan. 1, 2019, the threshold on medical expense deductions is reduced to 7.5% for all taxpayers. In addition, the rule limiting the medical expense deduction for AMT purposes to 10% of AGI doesn't apply to tax years beginning after Dec. 31, 2016 and ending before Jan. 1, 2019.