Time and a half of $21 an hour comes out to $31.50: multiply $21 by 1.5, or equivalently add half of $21 ($10.50) to the base wage. Under the FLSA, that's the minimum rate for hours worked past 40 in a workweek for non-exempt employees.
In real paycheck terms, a 45-hour week at this wage grosses $998 versus $840 for a standard 40 — the five overtime hours pay $158, as much as 7.5 regular hours. That leverage is why overtime shifts at $21/hour move a budget faster than the base rate suggests.
Working these hours in 2025–2028? The $10.50/hour premium portion may be federally deductible — see the no tax on overtime calculator. And if your employer pays 2x for some hours, that's $42.00/hour — the double time calculator covers it.