Can I still contribute to retirement and get the deduction IF I filed for an extension (does the retirement incentive deadline get moved up to October with the file deadline?)

[DoninGA]

The last date to contribute to an IRA for tax year 2016 would be on April 18, 2017.  An extension request does not give you an extra six months to contribute to an IRA for 2016.  Any contributions after April 18, 2017 would be reported on the tax year 2017 return filed during 2018.

https://www.irs.gov/publications/p590a/ch01.html#en_US_2016_publink1000230424

Contributions must be made by due date.   Contributions can be made to your traditional IRA for a year at any time during the year or by the due date for filing your return for that year, not including extensions. For most people, this means that contributions for 2016 must be made by April 18, 2017.

Due date for contributions.   Because April 15, 2017 falls on a Saturday, and Emancipation Day, a legal holiday in the District of Columbia is observed on Monday, April 17, 2017, the due date for making contributions for 2016 to your IRA is April 18, 2017, even if you do not live in the District of Columbia.

[dmertz]

DoninGA's answer applies to regular personal IRA contributions.  However, if you are asking about a self-employed retirement contribution, with a timely filed extension request a SEP plan can be established and a SEP IRA account opened and funded up until the extended filing deadline.  Similarly, the employer portion of a SIMPLE IRA or Individual 401(k) contribution can also be made up until the extended filing deadline provided that the either of these plans was established prior to the establishment deadline in 2016.

[CommunistFinanceBro]

Thanks for this informative reply. I have a further clarifying question which you perhaps can help with: what about the EMPLOYEE contribution to a 401(k)? My partner wants to set up payroll deductions to her plan but we always extend our taxes. Can she count her contributions between April and October toward the prior year's limit? If not, of course, she'll want to contribute more each paycheck. Thanks for any info you can provide.

[dmertz]

CommunistFinanceBro:  No.  Employee elective deferrals apply to the year of the earned income from which the elective deferral is made.  Elective deferrals from income earned in 2019 are 2019 elective deferrals.

For a self-employed individual, the election to make elective deferrals must be made by year-end and generally must be deposited by January 15 of the following year.  However, the deadline for making employer contributions is the due date of the tax return, including extensions.