You don't account for it on a 2017 tax return. You enter your non-deductible Traditional IRA contribution which will establish a basis in the IRA that will offset (or help offset) the taxable amount of the conversion when reported next year on your 2018 tax return.
2017 IRA *contributions* can be made before the April due date. Any 2017 *conversion* must have been completed before December, 31, 2017. A conversion in March of 2018 is 2018 conversion and will be reported next year you your 2018 tax return.
**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.**
