Why is my standard deduction for filing single only $4,662 this year and not the standard $12,400?

[Opus 17]

Are you someone's else's dependent?  Are you under age 19, or under age 24 while a full time student?  In those cases, your standard deduction is limited to your income earned from working plus $350.  This is due to the "kiddie tax" which is designed to prevent parents from putting investments in their children's names to avoid tax by using their child's standard deduction and lower tax rates to pay less tax on those investments.  the kiddie tax applies to all unearned income including investments, dividends and unemployment compensation. 

https://www.irs.gov/taxtopics/tc553

https://www.irs.gov/pub/irs-pdf/p501.pdf