From a large tax refund last year - to owing the IRS this year.. ?

Difference in income is only +5k over last year. difference in federal tax i payed is only +200 nothing's changed since last year, i have a dependant. Last year i received extra child credit for 600 this year did not. Last year i got a refund even without claiming my son, this year without his deductions i... show more Difference in income is only +5k over last year.
difference in federal tax i payed is only +200

nothing's changed since last year, i have a dependant. Last year i received extra child credit for 600 this year did not. Last year i got a refund even without claiming my son, this year without his deductions i would owe.

how is that possible when the income or taxes havent changed to a MAJOR degree...
Update: P.S. i owe over a thousand dollars this year.
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