hello, my mother has claimed my son for the past 3 years, we have lived with & I wasn't working so I let her claim him. Now for next years taxes 2021 I want to claim him since I started working, what can I do? I also want to be able to get the child tax credit but when I e-filed it said my sons SS was already on another person file.
If your mom claimed your child on her 2020 return you cannot e-file a return that claims him. Did she support him during 2020? If so then you wait and claim him on your 2021 return if you are now supporting him. If your mother did not support him in 2020 and you did, then mom can amend her return to remove him as her dependent ----but even if she amends her 2020 return you cannot e-file. If you claim him you can only file by mail now.
The new child tax credit monthly payments that start in July are a separate issue.
There will be a portal on the IRS site where you can claim your child for those payments---and where "Mom" can indicate that she does NOT want to receive those payments. The portal is not ready yet.
That CTC increase is not for 2020; it is for 2021. Your 2020 return does not have to be amended for it. More information will be available soon; the details of how it will be implemented have not yet been clarified fully. There will be monthly payments going out beginning in July 2021, with some of the CTC still left as a refundable credit on your 2021 tax return next year.
https://www.irs.gov/credits-deductions/advance-child-tax-credit-payments-in-2021
If you and your son live with your mother, then only one of you can claim the child as a dependent, including all dependent tax benefits including the child tax credit, ability to claim head of household status, and get the stimulus payments. You can't split the tax benefits of the child.
As the parent, you have the absolute first pick on claiming your child as a dependent. Your mother can only claim the child if you allow it and you don't claim the child, and if your mother's taxable income is higher than yours.
For 2020, the only way you can get the child tax credit and rebate is to claim your child as a dependent, in which case you will have to mail your return (since the e-filed return will be rejected). Your mother will have to file an amended return to remove the child as a dependent, and will have to repay any stimulus rebates, child tax credit, or other tax benefits that she got from claiming your son.
For 2021, you can just claim your child on your tax return, you don't have to do anything special even though you did not claim your child before. Your mother can't claim your child if you do, so you and your mother should be having a conversation about your tax situation so it doesn't come as a surprise.