What is $20 an hour with a $1 shift differential?

$20 an hour with a $1 shift differential pays $21 an hour on the shift. In a 48-hour week, 24 hours at $20 and 24 on the shift, the differential counts in the regular rate for overtime: $20.50 an hour, so the 8 hours over 40 add $82 and the week pays $1,066 before taxes.

Federal law (the FLSA) does not require extra pay for nights or weekends: the differential is an agreement with your employer. When you get one, it counts in the regular rate (29 CFR 778.207), which is the weighted average of your rates (29 CFR 778.115).