TurboTax never knows why the IRS reduced your refund, nor can TT find out for you. The IRS will mail you a letter in several weeks that explains what they changed and why. Possible reasons include back taxes you owed, child support owed, or---most commonly this year---a mixup regarding the stimulus payment you received last year. If you received the $1400 per person stimulus check last year and then answered the questions on your tax return about it incorrectly, it caused your refund to be reduced.
Check to see if you had a recovery rebate credit on line 30 of your Form 1040. Then check your online IRS account to see if the IRS says you received the stimulus money already and claimed it again on your tax return. And check for mistakes with the advance child tax credit payments too--another common source of confusion this year.
https://www.irs.gov/payments/your-online-account
If you still cannot figure it out, wait for your letter. If you think the IRS is wrong when you get the letter, there will be a way to dispute it with the IRS.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
