Inventory valuation determines the cost attached to closing inventory and to inventory issued during a period. For this topic, you must distinguish clearly between FIFO and AVCO and between perpetual and periodic systems.

Why inventory valuation matters

Inventory methods assign costs to units remaining in inventory after some units have been issued. The chosen method affects the value of closing inventory in the ledger and in financial statements. In cost accounting, it also affects the cost charged to production or to sales, so accuracy is essential. A small change in unit cost can produce a significant change in total inventory value when quantities are large.

When answering exam questions, always separate two decisions:

• which valuation basis is being used: FIFO or AVCO

• which inventory system is being used: perpetual or periodic

Inventory systems

Perpetual inventory system

When a business uses a perpetual inventory system, inventory records are updated after every receipt and issue.

Under this system, each movement is recorded in sequence. The order of purchases matters because the cost attached to an issue depends on the inventory balance immediately before that issue. This is especially important for AVCO, where the average cost may change several times during a period.

Periodic inventory system

A periodic inventory system updates the inventory record only at the end of the accounting period.

Under this system, purchases are accumulated during the period, and closing inventory is valued only after total units available and total units remaining are known. Physical counting at period end is therefore crucial because the closing quantity is determined then. Because no running balance is kept for each issue, the timing of issues within the period does not affect a periodic AVCO calculation.

FIFO

With first in, first out (FIFO), the earliest cost is assigned first when inventory is issued, so the oldest units are treated as leaving inventory before newer units. FIFO therefore works through inventory in cost layers, starting with the oldest layer available.

Worked FIFO illustration showing multiple purchase lots (“cost layers”) and the rule that the unit issued is valued from the earliest lot first. This helps students visualise how FIFO pulls costs from the oldest layer before moving to later layers when required. Source

In a perpetual FIFO system, each issue is priced from the oldest cost layers still in hand at that date. If the issue is larger than the quantity in the oldest layer, the valuation moves to the next oldest layer, and so on. Closing inventory is therefore made up of the most recent purchase costs still in inventory at the end.

In a periodic FIFO system, the same basic idea is applied at the end of the period. Since the oldest units are assumed to have been issued first, the units remaining in closing inventory are valued using the latest purchase costs available. In many exam questions, FIFO gives the same final closing inventory figure under both perpetual and periodic systems, provided the inventory data are complete and consistent.

When prices are rising, FIFO usually gives a higher closing inventory value because the newest, higher costs remain in inventory. When prices are falling, the opposite tendency appears.

AVCO

With average cost (AVCO), each unit is valued at an average cost rather than at a specific purchase price.

This method smooths out price fluctuations because high and low purchase prices are blended into one average figure. It is called a weighted average because quantities bought at each price influence the final average.

Weighted-average (AVCO) illustration combining several purchase lots into a single average unit cost (shown as a computed figure for one unit). It reinforces that AVCO blends costs across quantities rather than tracking individual cost layers like FIFO. Source

Under a periodic AVCO system, one weighted average cost is calculated for the whole period using opening inventory and all purchases made during the period.

Formula diagram summarising the periodic weighted-average cost per unit as “cost of goods available for sale ÷ units available for sale.” It provides a fast check that the AVCO unit cost is computed as a single blended rate before valuing closing inventory. Source

After this average has been found, the closing inventory units are multiplied by the average unit cost. Because the average is calculated once, after all purchases have been considered, the timing of issues during the period does not change the average.

Under a perpetual AVCO system, a new weighted average cost is calculated each time additional inventory is received. This is often called a moving average. Each issue is then valued using the current average cost in the inventory record at that moment. As a result, the average can change several times in one period, and the closing inventory value may differ from the value produced by periodic AVCO.

What to focus on in exam questions

• Read carefully to identify whether the question requires perpetual or periodic valuation.

• For FIFO, track cost layers in date order.

• For periodic AVCO, combine opening inventory with all purchases before calculating one average cost.

• For perpetual AVCO, recalculate the average only after each receipt, not after each issue.

• Closing inventory is valued from the units left at the end, so quantity accuracy matters as much as cost accuracy.

• Keep units and costs separate in your working: first determine remaining quantities, then apply the correct valuation basis.

• If purchase prices change during the period, expect FIFO and AVCO to produce different inventory values.

• Present workings clearly, because marks are often awarded for method as well as the final figure.