@GreyGrey
The filing requirements for a dependent are different from someone who is not a dependent. You really need to sit down and figure out whether you are required to file for 2018, 2019, and 2020. You can use the online tool at the following link on the IRS web site to figure that out for 2018 and 2019. You'll make the determination for 2020 after the year ends.
Do I Need to File a Tax Return?
You can always file a tax return, even if you are not required to file. There are a number of reasons that you might want to do that. One possible reason is to carry over a capital loss. As stated earlier, in order to carry over the loss you have to file for the year the loss occurred and every subsequent year until the loss is used up.
You said you have some capital gains in 2020, so you most likely do have to file for 2020. You should probably file even if you technically don't have to. The only change in the filing requirements between 2019 and 2020 is some small inflation adjustments. You could get a pretty good idea of whether you have to file by putting your 2020 information into the IRS tool and selecting 2019 as the year if they have not yet updated it for 2020.
It's not clear whether the IRS knows that you had losses in 2018. It depends on whether the basis of the investments that you sold was reported to the IRS. The Form 1099-B or equivalent statement from the brokerage or mutual fund tells you whether the basis was reported. If the basis was not reported, the IRS sees only the proceeds of the sale, but not what you originally paid for the investments. Without the basis, it looks to the IRS like the proceeds are all taxable income, and they will eventually come after you to pay tax on the full amount of the sales.
When you haven't filed a tax return, there is no statute of limitations for that year. The IRS can look back as many years as they want to, and come after you many years later. (Another of the reasons to file when not required to is to start the clock running on the statute of limitations.) If it turns out that you were required to file, and you owe tax, you will also be hit with penalties and interest. The sooner you file the better.
@GreyGrey wrote:
Would it be simpler if I just leave 2018 losses alone and start off fresh? In the long run, I'm not going to lose sleep over the losses anyway.
It certainly would be simpler to forget about your 2018 losses, provided that you are not required to file for 2018. You could do that if you feel that the losses are not enough to "lose sleep over." You haven't said how much the losses are, or how much income you have in 2020. But you started off asking whether you could use the earlier losses to offset this year's gains, so that suggests that it would make a difference to you.
