It does not matter when the tax return is filed as long as the contribution is made on or before Apr 15. (If a Traditional IRA and it was not reported on a previously filed tax return then it would be necessary to amend to add it within 3 years of the filing date.)
Or you can make a 2018 Roth IRA contribution up to April 15, 2019 and nothing needs to be entered on your tax return at all* - only Traditional IRA contribution must be entered.
*You might want to enter the Roth contribution into TurboTax anyway to:
1) Tell you if your income qualifies you for a contribution and warn you if it does not.
2) Check if your income exceeds the limit to contribute to a Roth.
3) Track your contribution year-to-year if you use TurboTax every year.
4) Add the Retirement Savers Credit if you qualify.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
