You are correct in your assumption. You can only deduct what you actually paid. You do not need to make any calculations. Follow the steps below.
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Enter the health insurance premium information from your 1095-A on the 1095-A screen in TurboTax. This is information will be used in Form 8962 to determine any adjustment needed in the premium tax credit your received. Form 8962 Line 26 will show the resulting over/under tax credit and be transferred to your 1040.
