Many families have children heading back to school this month. It is not uncommon for a nanny who cares for both an elementary school child and a pre-schooler or younger to negotiate two different hourly rates - one for one child only, the other for both. The puzzle for many nanny employers is how to calculate the correct overtime rate. Legally, the "regular rate of pay," that which is used to calculate the overtime differential, must be at least the weighed average of all rates used in the work week. Here is an example: