By what date do I need to contribute to my IRA to get the deduction?
Contributions can be made to your Traditional IRA at any time during the year, or by the due date for filing your tax return in the year following that tax year (not including extensions), usually April 15th. If April 15 falls on a weekend or a legal holiday, the contribution must be made by the next working day. (For tax year 2015, your tax return is due April 18, 2016.)
If you contribute between Jan. 1 and April 18, be sure to identify to the financial institution that the contribution payment is being made for the 2015 tax year, and not for the current 2016 calendar year. You can claim a deductible contribution or report a non-deductible contribution (Form 8606) on your return even if you haven't made the contribution yet, provided you make the IRA contribution (it is funded) by the return's due date.