The wholesale price plus portion of fixed overheads ( rent,rates, utility costs, wages , etc.). The longer an item remains in stock ,the more the shelf price rises ,eating into the margin to retail price ,thereby reducing gross profit on cost. The quicker an item sells then the lower the fixed overheads and the lower a gross profit on cost is tolerated e.g. perishables (bread,newspapers) compared with slow items such as clothes where the gross profit on cost is much higher as they may take several weeks to sell making the gross profit on return more comparable