COGS and Inventory: Reconcile Opening Stock, Purchases and Closing Stock

Cost of goods sold links inventory records to profit. Under a simple periodic model, goods available for sale are opening inventory plus purchases, and the unsold closing inventory is deducted. All figures must use a compatible cost basis.

Work through the inventory bridge

Suppose opening inventory is $5,000, purchases are $12,000 and closing inventory is $4,000. Goods available cost $17,000. Subtracting the $4,000 remaining inventory gives $13,000 COGS.

If revenue is $20,000, gross profit is $20,000 − $13,000 = $7,000 and gross margin is 35%. This example does not calculate operating expenses, taxes or net profit.

Use cost rather than selling value

An item purchased for $20 and offered for $50 should not be valued at its $50 retail price in this simplified cost reconciliation. Mixing retail and purchase values can produce a distorted or even negative result.

Purchases also need the adjustments appropriate to your records, such as returns to suppliers or relevant landed costs. The calculator cannot infer adjustments missing from the input totals.

Understand the effect of a stock-count error

If closing inventory is mistakenly recorded as $5,000 instead of $4,000, COGS becomes $12,000 rather than $13,000. Gross profit is overstated by $1,000.

That is why a margin improvement should sometimes prompt an inventory review rather than immediate celebration. Count accuracy, timing cutoffs and valuation consistency influence the result.

Check unusual outputs before using them

Closing inventory greater than opening inventory plus entered purchases produces negative COGS in this basic formula. Investigate omitted receipts, valuation differences, transfers and period mismatches. Do not interpret the negative number as a normal operating improvement.

The simple equation does not model every manufacturing or accounting adjustment. More complex records may include work in progress, write-downs or other movements that need professional treatment.

Keep timing and documentation aligned

Use balances at the beginning and end of the exact reporting period. A stock count performed several days after month-end needs reconciliation for intervening receipts and sales; otherwise the cost bridge mixes different periods.

Use the COGS Calculator to check arithmetic, then the Gross Profit Calculator. Review the Inventory Turnover Calculator only after confirming the inventory values are comparable.

Related reading

Continue with Inventory Turnover and Inventory Days: Handle Seasonality Correctly for another part of the calculation.