Can I amend tax returns for capital loss?

[BC1231]

For a married filing jointly tax return, if one spouse didn't include 1099 capital short term stock losses of $10,000 in the tax filing for the year of the loss, can that loss be filed for in a subsequent tax return, or is the previous years tax supposed to be amended. For example, if the loss was in the 2020 year and wasn't included in the 2020 filing, can it be amended or added on to next years tax filing? If so, how would the carryback be calculated and would it be "refunded"?  

If they had a taxable income of $30,000 in 2020 with no capital loss deducted and a standard deduction of $12,400 already applied, does that mean a further $3000 in capital loss can be deducted from the $30,000? Does that change their Tax Table from $30,000 to $27,000 and the IRS refund the difference? 

[fanfare]

you can deduct the $3,000 (max) of your loss.

You have to amend the tax return for the year of the loss,

unused losses carry forward to the next tax years.

[VolvoGirl]

Yes you should amend to add the sales to 2020.  The IRS will be looking for it.  Did you report any gains for 2020?  You need to amend to calculate the right amount of loss to carry forward to 2021.  Yes you might get a little refund from it.  

If you filed Married Joint the Standard Deduction is 24,800.

How to Amend 2020

https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-return/00/27439