What is a 10% shift differential on $15 an hour?

A 10% shift differential on $15 an hour adds $1.50 an hour, so the shift pays $16.50 an hour. In a 48-hour week, 24 hours at $15 and 24 on the shift, the differential counts in the regular rate for overtime: $15.75 an hour, so the 8 hours over 40 add $63 and the week pays $819 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).