If I elect to NOT use Pre-TCJA rules, as far as I understand unearned income would be taxed at the trusts and estates rate. This wouldn't depend on my parents income or anything of the sorts, but the 8615 form still asks for that information (parents taxable income, parents qualified dividends, and parents capital gains).
I don't have that information on hand and my parents might not have it for a decent while (and might file for an extension), and I'm wondering if it's actually necessary for me to enter completely accurate information in those fields, or if ballparks are good enough.
That's a known bug in the TurboTax interview. It shouldn't be asking for your parents' information at all if you are not using the pre-TCJA rules. But it does the tax calculation correctly using the new rules. So you can enter anything you like just to get through the questions. It doesn't even have to be in the ballpark. TurboTax is not going to use the parents' information that you enter.
That's a known bug in the TurboTax interview. It shouldn't be asking for your parents' information at all if you are not using the pre-TCJA rules. But it does the tax calculation correctly using the new rules. So you can enter anything you like just to get through the questions. It doesn't even have to be in the ballpark. TurboTax is not going to use the parents' information that you enter.
Ah, that makes sense.
I was also wondering if you could help me understand how the tax amount it calculates is done. It seems much lower than what I would've expected. In the tax smart worksheet section of my 1040 it also lists the tax as being calculated from Form 8615.
Even if I used my single tax bracket rates on my taxable income (11a) I would get a higher number than what it lists. And as I understand it, it should be even higher than my single tax bracket rate as the trust and estate rate is much higher than my single rate (for the portion that is unearned income).
Unfortunately, it is still required. Please see this answer from KatrinaB.
You are required to enter your parent's income tax information because it is used to calculate the amount of tax due. When filing your return you are required to report your parent's information as stated below:
Please view this TurboTax Page for more information about figuring the tax on form 8615.
I'm pretty sure the information isn't used to calculate the tax rates though. The TCJA changes made it so the tax rate was based on trust and estates, no? I assumed that was the whole point of the "Do you want to use pre-TCJA rules or not" question. If you used pre-TCJA rules, then it's taxed at a parents rate, but otherwise it would be taxed at the rate of trusts and estates.
https://www.irs.gov/taxtopics/tc553
"If your child's interest, dividends, and other unearned income total more than $2,200, it may be subject to tax. The unearned income of certain children is taxed using the tax brackets and rates for estates and trusts unless an election is made to calculate the child's tax based on the parent's tax rate."