I made a mistake in using Turbotax where I added my self-employed consulting income twice. This resulted in greater taxes, but also an excess SEP IRA contribution. I am working on the 2015 1040X. Do I need to fill out a 5329 or 5330 for 2015? I am hoping I can do the 1040X with the corrected income and file with the correct SEP IRA contribution. I hope to then decrease my 2016 SEP IRA contribution. Does this sound correct?
Since your SEP contribution was made in March 2016, you can allocate the portion that was not a deductible contribution for 2015 as a contribution for 2016 instead. The SEP-IRA custodian only tracks and reports the year in which a contribution is made, not for which the contribution is made. It's your responsibility to track the year for which contributions are made. If your 2016 self-employment profit is sufficient, you should end up with no nondeductible contribution that would need to be reported on Form 5330.
Since your SEP contribution was made in March 2016, you can allocate the portion that was not a deductible contribution for 2015 as a contribution for 2016 instead. The SEP-IRA custodian only tracks and reports the year in which a contribution is made, not for which the contribution is made. It's your responsibility to track the year for which contributions are made. If your 2016 self-employment profit is sufficient, you should end up with no nondeductible contribution that would need to be reported on Form 5330.