I entered $3562 into my Self-Employment income and my Federal Refund dropped by $821, but 15.3% of $3562 is only $544.83. So why did my refund drop by $276.17 extra?

[jasminerosenstie]

It was for delivering food via Grubhub and Doordash

[SweetieJean]

Well, you also owe regular tax on that $3562.

And, in general, whenever you add income of any type, some of your deductions/credits can be reduced or eliminated.