| Is isn't the same question. This one is asking specifically for how to calculate cost of goods sold, and the other is a vague question about how to do all accounting procedures for all inventory methods.
Cost of goods sold isn't "calculated" using a perpetual system. Every time something is sold, its cost is credited out of merchandise inventory and debited into cost of goods sold. At the end of the period, the balance in that account is your cost of goods sold. If you call balancing a ledger account "calculating" it, then that's how. | 
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