You can only enter on the 2021 tax return the amount of medical expenses you actually paid in 2021. When you file your 2022 tax return in 2023 you can then enter the amount of medical expenses you paid in 2022.
Medical expenses are entered on Schedule A as an itemized deduction. Only the amount of medical expenses which exceeds 7.5% of your Adjusted Gross Income (AGI) can be entered on Schedule A as a medical expense.
