what is one primary difference between determining cost of goods sold with a periodic system rather than a perpetual system? with a periodic system, cost of goods sold is calculated only once per day. in contrast, with a perpetual system, cost of goods sold is recorded each time a sale is made. with a periodic system, cost of goods sold is calculated only once at the end of the period. in contrast, with a perpetual system, cost of goods sold is recorded each time a sale is made. with a periodic system, cost of goods sold is recorded each time a sale is made. in contrast, with a perpetual system, cost of goods sold is only calculated once at the end of the period. with a periodic system, cost of goods sold is recorded each time a sale is made. in contrast, with a perpetual system, cost of goods sold is only calculated once per day.