The simple answer is: when box 5 exceeds box 1 by more than $12,200.
Everybody gets a (potential) $12,200 standard deduction, even student-dependents*. So, if you have less than $12,200 total taxable income, you will owe no tax and do not even have to file a tax return
*There is an exception for dependents with investment income (interest, dividends, capital gains and taxable 529 plan distributions)
