I'm unable to file my 2016 return through the site. I know I'm very late, but my son didn't have a SSN and I have all required documents now. Am I able to use TurboTax?

[vickersjarrod]

What's the best way for me to file for last year's return, and what kind of penalties can I expect?

[fanfare]

Only one way: on paper via US Mail.

You can still use TurboTax CD/Download version. If you expect a refund, relax there will be no penalties.

[VolvoGirl]

You have to buy the Desktop CD/Download program here https://turbotax.intuit.com/personal-taxes/past-years-products/  

   Or you can get the blank forms from the IRS and do them by hand.  Either way you will have to print and mail prior year returns.  And send each year in a separate envelope so the IRS doesn't miss any.

Here are some blank forms & instructions for 2016
1040 https://www.irs.gov/pub/irs-prior/f1040--2016.pdf     
Instructions https://www.irs.gov/pub/irs-prior/i1040gi--2016.pdf

1040A https://www.irs.gov/pub/irs-prior/f1040a--2016.pdf    
Instructions https://www.irs.gov/pub/irs-prior/i1040a--2016.pdf

1040EZ https://www.irs.gov/pub/irs-prior/f1040ez--2016.pdf    
Instructions https://www.irs.gov/pub/irs-prior/i1040ez--2016.pdf

2016 Tax Tables https://www.irs.gov/pub/irs-prior/i1040tt--2016.pdf
Publication 17 Tax Guide for 2016 https://www.irs.gov/pub/irs-prior/p17--2016.pdf