The gross profit method is a technique for estimating the amount of ending inventory. The gross profit method might be used to estimate each month's ending inventory or it might be used as part of a calculation to determine the approximate amount of inventory that has been lost due to theft, fire, or other causes.

The gross profit method of estimating ending inventory assumes that we know the gross profit percentage or gross margin ratio. For example, if a company purchases goods for $80 and sells them for $100, its gross profit is $20 and it has a gross profit percentage or ratio of 20% of the selling price. When this company has sales of $50,000 it is assumed that its cost of those goods will be $40,000 ($50,000 minus 20% of $50,000;  or 80% of $50,000).

Let's assume we need to estimate the cost of the July 31 inventory. The last time the merchandise inventory was counted was seven months earlier on December 31 and it had a cost of $15,000. Since December 31, the company purchased merchandise with a cost of $42,000; its sales were $50,000; and the gross profit percentage has remained at 20%. We can estimate the July 31 inventory as follows:

Inventory cost at December 31:  $15,000

Purchases between December 31 and July 31 at cost:  $42,000

Expected cost of goods available:  $57,000 ($15,000 + $42,000)

Cost of goods sold: $50,000 of sales  x 80% = $40,000

Estimated Inventory at July 31 at cost:  $17,000 ($57,000 - $40,000)