Cfa笔记inventories

计算inventory成本的四种方法，本质上是在把inventory cost在资产负债表的inventory和损益表的cost of sales之间分配。

IFRS支持specific identification, first-in, first-out (FIFO), 和weighted average cost。GAAP额外支持LIFO，但是要求披露“跟采用FIFO之间的差额”。

Specific identification通常用于not interchangeable的商品，而其他三种则是用于interchangeable的，而且具有assumption性质。

cost of inventories

The costs to include in inventories are “all costs of purchase, costs of conversion, and other costs incurred in bringing the inventories to their present location and condition.”常见的包括买价、运输成本、进口税和各种税等等。但是不包括：

1. abnormal costs incurred as a result of waste of materials，比如残次废品的原材料成本和制造费用都是要费用化（be expensed）的
2. storage cost
3. all administrative overhead and selling costs

把不该算作cost of inventories的费用包含进去会导致当期profit虚增和asset虚高。

Specific Identification

用于not ordinarily interchangeable和produced and segregated for specific projects的产品，特别是expensive goods比如宝石。

Wighted Average Cost

LIFO和FIFO

LIFO的inventory是最先购买/生产的商品，而FIFO则反过来，所以有以下通用规律：市场价格上升时，LIFO分配的cost of sales > inventory，所以gross profit, net income, assets都低，但是net operating cash flow得到增益（因为income tax expense更低），显得更valuable

LIFO的效果

如果inventory costs在上升，那么会带来potential income tax savings.具体来说：

1. income statement：
   1. higher costs of sales
   2. lower: gross profit, operating profit
   3. lower income tax expense (but higher net cash flow from operating)
   4. lower net income
2. balance sheet:
   1. lower: ending inventory, working capital, lower total assets
3. Ratios:
   1. lower: current ratio, profitability ratio，存活周转天数
   2. higher: debt-to-equity ratio, 存货周转率，毛利率、净利率、ROA

LIFO reserve

长：The difference between the reported LIFO inventory carrying amount and the inventory amount that would have been reported if the FIFO method had been used

短：$\text{FIFO} - \text{LIFO}$

（在units不变或者增加的情况下）如果成本在increasing，那么reserve就会上升；如果reserve是increasing，那么cost of sales的调整就是substract the increase。

LIFO Liquidation

如果卖的比产的多，就会出现LIFO liquidation。如果成本在increasing，就会带来（不可持续的）inventory-related increase in gross profits.

管理层可以故意促使liquidation发生，从而实现虚高的收入。需要检查LIFO reserve的披露来确定是否有这种现象。

如何计算

直观法：

1. $ \text{本来应该的成本} = \text{units sold} \times \text{current purchase cost per unit} $
2. gross profit due to LIFO liquidation: $ \text{本来应该的成本}-\text{报表的成本} $

间接法：

1. 计算出用了多少库存单位
2. 用 $ 库存单位 \times (\text{本期购买成本}-\text{库存单位的购买成本}) $

Periodic/Perpetual System

对于periodic system, inventory values和costs of sales是在会计周期结束的时候确定的；买来的商品会记录在purchase账户里，买来的+期初库存=当期available for sale的商品数；期末inventory则是通过现场清点的方式得到。而perpetual则是根据买卖实时更新。

疑惑记录

Under a periodic inventory system, the amount of cost of goods available for sale allocated to cost of sales and ending inventory may be quite different using the FIFO method compared to the weighted average cost method. Under a perpetual inventory system, inventory values and cost of sales are continuously updated to reflect purchases and sales. As a result, the amount of cost of goods available for sale allocated to cost of sales and ending inventory is similar under the FIFO and weighted average cost methods.

可以通过极限的方式来理解：如果把periodic的周期缩短到无限小，那么就等于perpetual了。造成区别的核心原因在于weighted average是周期末才“大锅饭”算一次，如果一个周期里面成本多次波动造成每批次产品的cost不同，weighted的精度就不够了。

速食结论：FIFO下任意一种系统都一样；LIFO下会不同特别是涉及liquidation的时候。

Measurement

IFRS：Inventory需要按照 $ min(\text{cost}, \text{net realisable value}) $ 来记录。

Net realisable value is the estimated selling price in the ordinary course of business less the estimated costs necessary to make the sale and estimated costs to get the inventory in condition for sale.

GAAP：非LIFO和retail inventory methods用 $min(\text{cost}, \text{net realisable value})$ ，否则用 $min(\text{cost}, \text{market value})$

Market value is defined as current replacement cost subject to upper and lower limits. Market value cannot exceed net realisable value (selling price less reasonably estimated costs of completion and disposal). The lower limit of market value is net realisable value less a normal profit margin.

例外：agricultural and forest products、minerals and mineral products、commodity broker–traders的inventory使用net realisable value计算，价值增减直接算进gain or loss。

Write down和Reversal

net realisable value低于cost的时候，要把inventory的carrying amount减少到net realisable value，然后将这个差值写在income statement的expense（cost of sales）里。

IFRS Reversal: 上限是把当初的write-down的金额，不能多reverse。reverse的amount应该减记当期cost of sales。

GAAP：不允许reverse。

相比其他三种计算方式，LIFO通常来说发生write-down的可能性比较小（因为物价一般都在涨）。

相关公式

从LIFO调节为FIFO

根据披露能够得到LIFO reserve.

ending inventory：LIFO + reserve

cost of sale: $\text{LIFO} - \Delta \text{reserve}$ ¹

net income: $\text{LIFO} + (\Delta \text{reserve}) \times (1-\text{tax rate})$

net cash flow from operating activities: $\text{LIFO} - \Delta \text{reserve} \times \text{tax rate}$²

cumulative amount of income tax savings：$\Sigma^n_1{\Delta \text{reserve}_{year} \times \text{tax rate}_{year}}$ ³

retained earnings: LIFO + reserve - cumulative amount of income tax savings

对balance的影响：inventory增加reserve，deffered tax liability增加cumulative amount of income tax savings，equity增加两者的差值（也就是retained earnings）。