On your 2018 tax return you can claim only medical expenses that you actually paid in 2018, not amounts that you owed but did not yet pay by the end of 2018. Also, you cannot claim any amount that you were reimbursed for. If you have more than one medical insurance policy, one policy might reimburse you for amounts that were deductibles or copays on the other policy.
Medical expenses are an itemized deduction with a 7.5% of AGI limitation. You enter the full amount that you actually paid. The amount of your actual deduction will be the full amount minus 7.5% of your Adjusted Gross Income (AGI). TurboTax will do the subtraction. Furthermore, the deduction will not make any difference in your tax unless your total itemized deductions are more than your standard deduction. It's possible that, even with a lot of out-of-pocket medical expenses, the deduction will not make any difference in your tax.
