Normally, engagements are either per effort or annually.
Per effort tasks are charged at an agreed-upon rate per person, plus expenses. Invoices are submitted monthly, with payment due within 45 days.
Availability of most CSSCS personnel is limited. Thus, an initial retainer is required, with initial billing charged against it; early termination of the engagement forfeits any unused portion of the retainer. Invoices are billed against the first 80% of the retainer, with the remainder used to settle the final billing.
Annual engagements (e.g., advisory boards) are on an annual fee basis for predefined involvement, plus any expenses. Annual engagements are billed quarterly or pre-billed annually, as the client wishes.