I am just finding out I could have declared interest on my Time share, but didn't in the year 2015. Can I still do this and how ? I did use Turbo tax .

[bwa · Accepted solution]

You can still do it, but it needs to be done by filing an amended return (Form 1040-X) on paper for 2015.

Amended returns for prior years can only be prepared with the desktop version of Turbotax, and can only be filed by mail. If the amended return is for a refund, the IRS currently takes from 12 - 16 weeks to process amended returns and issue them. Depending on what is adjusted, amending a federal return may also require you to amend your state return, if the change also effects your state taxable income.

See this TurboTax site on how to amend:  https://ttlc.intuit.com/questions/1894381

[If you paid for TurboTax on-line to prepare your prior year return and need to amend it, TurboTax might be able to provide you with a free copy of the desktop program for that year. To get a number for TurboTax support, go to https://.intuit.com/support/contact/index.jsp?msid=int_hp_call, select a topic and subtopic, and you will be provided a telephone number to call (Note:  Telephone numbers are only given when TT support is open.  See this URL for hours of operation.  https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number?jump_to=answer_3300041 Please note that times given are Pacific Time.)