Prorate Partial Periods determines how the system handles partial periods that do not fit into a monthly cycle. In the previous example, if this field is Yes, the system generates a separate invoice for the period of January 15 through January 31. From that point on, invoicing is synchronized with the first of the month: The system creates a prorated invoice again at the end of the year for the period January 1 through January 14.

If Prorate Partial Periods is No and Period Based Billing is Yes, the covered days that do not fit cleanly within a month are essentially given away. If you want to ensure complete invoicing, set Prorate Partial Periods to Yes.

Partial billing periods can result when Period Based Billing is Yes, but they may also occur if contract start and end dates do not follow monthly cycles. For example, if Period Based Billing is No and you have a contract from January 22 to April 5, the system bills for two full months from January 22 to February 21, and February 22 to March 21. This leaves 15 days of coverage.

The price for coverage is in terms of monthly units. To determine the price for a number of days less than a month, the system uses the number of days in the month of the last coverage day. In the previous example, the last day of coverage is April 5. April has 30 days. So the prorated price is 15 divided by 30, resulting in 0.5 months. If the last day of coverage was May 5, the calculation would use 31 days and have a slightly different result.

The header start and end date determine the billing periods for a contract. The system then attempts to fit each line within the periods defined by the header. If a contract line begins or ends on a different day than the contract header, this can result in partial periods for the line that are then either dropped or prorated, depending on the control program settings.

For example, a contract has header dates of January 15 to March 14 and a monthly billing cycle. Period Based Billing and Bill Arrears are both No. The billing periods for the contract would be January 15 to February 14 and February 15 to March 14. The system bases line-item billing on the same periods.

The first line item on the contract has start and end dates of February 1 to February 28. The system bills this as two partial periods using the header billing periods. The system bills line coverage for February 1 to February 14 in the first period and coverage for February 15 to February 28 in the second period. If Prorate Partial Periods is No, this line would generate a 0 invoice amount during both periods, even though it appears to be for a month.