Final answer:
The lookback period used to determine an employer's deposit schedule is the four calendar quarters ending on June 30th of the previous year.
Step-by-step explanation:
The lookback period used to determine if an employer is a monthly or semiweekly depositor for the year 2016 is the four calendar quarters ending on June 30th of the previous year. This means that for 2016, the lookback period would be the four quarters from July 1, 2014, to June 30, 2015. During this lookback period, employers calculate the total payroll taxes they owe and determine if they fall into the monthly or semiweekly deposit schedule.