Is the medicare part B premiums considered as a net benefits in box 5 or are those premiums not reported as income on the tax return?

The net benefits in box 5 of the SSA-1099 is the amount that you received in 2017.  Any medicare premiums paid for part B would be entered as an itemized deduction on Schedule A.  Just enter the SSA-1099 as received and if the medicare part B premiums are shown in the Description of Amount in Box 3 then enter those in the space provided on the TurboTax screen for SSA-1099.  Do not enter the premiums paid again in the Medical Expenses section since the program has already entered those expenses on Schedule A.

To enter Social Security benefits reported on form SSA-1099

• Click on Federal Taxes (Personal using Home and Business)
• Click on Wages and Income (Personal Income using Home and Business)
• Click on I'll choose what I work on (if shown)
• Scroll down to Retirement Plans and Social Security
• On Social Security (SSA-1099, RRB-1099), click the start or update button

Or enter social security benefits in the Search box located in the upper right of the program screen.  Click on Jump to social security benefits