Final answer:
Postings to control accounts in a costing system are typically done monthly to maintain accurate accounting records and enable manageable reconciliation.
Step-by-step explanation:
The question asks about the frequency of postings to control accounts in a costing system. Postings to control accounts are usually done on a monthly basis. This periodic posting helps in maintaining the accuracy of accounting records while providing a manageable timeline for reconciling the detailed subsidiary ledger to the control account in the general ledger. Daily postings would be too frequent and potentially burdensome, while annual or semi-annual postings could result in a lag in recognizing important financial information which could be detrimental for timely decision making.