USA Prepaid tax?

[FltCpt]

I have a bit of gain in the stock market this year, but my broker would not do tax withholding for me.
I worry that I have gone over the limit and incur tax penalty next year (because I had not
paid enough tax withholding).

Does anybody know if there is an IRS tax form that I can just fill out and then mail them a check
in advance within this year or so, kind of like my own withholding? If I just mail them a check cold
(I dont have any other information) will they know what to do with it?

Any advice will be appreciated, thanks!

 

[kirby]

Sure .On internet lookup " irs form 1040-rs for 2018". Download the form and follow the directions. You should do the same for your state taxes too.

 

[bklynboy]

Not aware of tax withholding on personal stock transactions. I don't think there is any penalty either. Unless you are sure you will be penalized just pay the tax when you file in April - no need to give them more money.

I would also look into whether you have any securities in a loss that can be sold to mitigate the tax - these should be stocks you plan to sell anyway but time it this year so you can reduce your capital gains tax on appreciated sales.