During 2018 I converted my regular IRA to Roth IRA and I already filed my 2018 personal tax return using 1099-R I received. My return are accepted and I already received refund from both federal and state on 5/15/2019. However, I just received form 5498 from my brokerage and found I put wrong numbers of Fair market value of all investment in my account at year end "box 5 in f5498". When I entered the right amount in TurboTax, I am entitled more refund. My question is how long should I wait before I can file amendment 1040X. Is there any earliest day I can file?
If the difference is not very large, you don't have to amend,
you will get your tax break over time as you take a distribution or do another conversion.
If the correct refund is very important to you you can amend now; IRS has finished processing your return.