Stock cost methods: 3 compared, 6 choice questions

Why the cost method matters

A stock cost method is the rule that decides which purchase price goes against each sale: FIFO, LIFO or weighted average. It is also called an inventory costing method. That one decision flows into your cost of goods sold, your gross profit, the value of the stock still on your shelves and, eventually, the tax you pay.

If prices never moved, the choice would hardly matter. They do move. Two businesses that sell identical goods at identical prices can report different profits simply because they chose different methods. Bookkeepers and owners therefore need to understand the options, pick one on purpose and apply it the same way every period.

This post covers the three methods you will meet most often: first in, first out (FIFO), last in, first out (LIFO) and weighted average cost. Each section explains how a method works, walks through a simple example and says what it means in practice. Later sections compare all three using the same purchases, offer a checklist for choosing and list habits that keep your records clean.

One caution before we start. The methods you may use depend on the accounting framework you follow, the tax rules where you operate and sometimes the type of business you run. This post explains how the methods work. It is not advice about your own filings, so confirm your choice with your accountant or tax adviser before you commit.

Guides also age. A Journal of Accountancy article on employer identification numbers warns readers: "The content may be out of date and links may no longer function." Its archived items carry a further note: "Please note: This item is from our archives and was published in 2019." Check the date on any guide, this one included, and confirm the current rules before you act on what it says.

FIFO: first in, first out

FIFO assumes that the stock you bought first is the stock you sell first. FreshBooks describes the idea simply: "It assumes that a business always sells its oldest products first."

In practice, each sale is costed from your oldest purchase batch. When that batch runs out, the rest of the sale draws on the next oldest batch, and so on. Your records must show which batch each unit came from. Once you see the logic working on a real order, it is easy to follow.

Take the pharmacy example from Xero's guide to the FIFO method. A pharmacy receives 100 units of a medication in January at $8 each and 100 more in March at $8.50 each. Later, 120 units are dispensed. FIFO assigns the first 100 units at $8 and the next 20 at $8.50. The rest of the March batch stays in stock at $8.50 each.

Why do businesses like it? The FreshBooks guide lists three advantages: "Advantages of FIFO include cost accuracy, simplicity, and regulatory compliance." It also calls FIFO "straightforward and intuitive, making it popular as an accounting method and useful for investors and business owners trying to assess a company’s profits." The records are easy to read, a bank manager can follow them, and the method often matches how perishable and time-sensitive goods physically move.

FIFO also shapes your numbers. When prices rise, the older and cheaper batches leave first, so cost of sales is lower and profit is higher than under LIFO. The stock on your shelves is valued closer to recent prices. When prices fall, the effect reverses, and the older and dearer batches leave first. Either way, FIFO ties your reported cost to the order in which goods arrived, not to what it would cost to replace them today.

LIFO: last in, first out

LIFO reverses the order. It assumes the newest purchases are sold first. In the words of FreshBooks, "An alternative method to FIFO is LIFO, or Last In, First Out." Each sale is costed from the most recent batch, and older batches stay in inventory at their older prices until the newer stock runs out.

Physical flow is the first hurdle. Few businesses sell their newest goods first, so LIFO often does not match how stock actually moves. Some owners still prefer it because it pairs recent costs with recent revenue, which they see as a closer picture of current economics. That reasoning is valid, but it is a different goal from tracking the physical order of goods. Be clear about which one you are after before you choose.

Here is the boutique example from Xero's FIFO guide: "A boutique orders 50 jackets in September at $40 each for the fall season, then another 50 in November at $45 each." If the boutique sells jackets from the November order first, LIFO costs those sales at $45 each, not at the September price of $40. The September jackets stay in stock at $40 until the newer order is used up.

When prices rise, LIFO usually shows a higher cost of sales and lower profit than FIFO would report for the same sales. The stock left on hand is valued at older, lower prices, which can understate what it would cost to buy again. That trade-off is one reason for care. LIFO should never be picked just to lower a tax bill.

Before you consider LIFO, check whether it is allowed for your business. Rules differ by jurisdiction and reporting framework, and moving into or out of LIFO can carry its own requirements. Get that answer in writing from your adviser before you change anything in your books.

Weighted average cost

Weighted average cost takes a different route. Rather than tracking batches, it blends them. Each time you buy stock, you recalculate one average cost for each unit by spreading the total value of the stock on hand across the units you hold. Each sale is then costed at the average in effect at that point.

The average is weighted by quantity, so a large batch pulls it further than a small one. That is what separates it from a simple average of the prices you paid.

Zoho's inventory valuation help page gives the basic relationship: the inventory asset value equals the stock on hand multiplied by the average cost of each unit. Keep that formula in mind when you check your inventory balance against your records.

Consider the furniture maker in the Xero guide. It buys lumber in two batches: 500 board feet in March at $3 a foot and 500 board feet in May at $3.50 a foot. Under weighted average, the cost for each board foot sold sits between $3 and $3.50, and it shifts as new purchases arrive. The maker never has to say whether a given board came from the March batch or the May batch. When the lumber is stored together, that saves a good deal of tracking.

The pharmacy works the same way. Weighted average would cost its 120 dispensed units at one average figure between $8 and $8.50, instead of splitting them into $8 and $8.50 portions. The total can differ from the FIFO total, because the average blends prices that FIFO keeps separate.

Weighted average has real strengths. It smooths out price swings, so one sharp rise or fall does not move your cost of sales as much. It gives you one unit cost to track for each item and needs less batch-level record keeping. It suits bulk goods that are mixed together, such as fasteners, grain or chemicals, where individual batches cannot be told apart once they are stored.

It has weaknesses too. The average changes with every purchase, so you must recalculate often, and a manual spreadsheet can become tedious for a busy stockroom. The average also lags behind a sharp price change, which means it may not reflect what you would pay to replace stock today.

The three methods side by side

The table uses the same general picture for each method. It simplifies, so treat it as a memory aid rather than a rulebook.

The pharmacy example makes the differences concrete. For the same 120 units dispensed, FIFO costs the first 100 at $8 and the next 20 at $8.50. LIFO works the other way and costs the 100 newest units at the March price of $8.50, with 20 units from the January batch at $8. Weighted average gives a single figure between $8 and $8.50 for all 120 units. The three methods generally produce different costs of sales for identical activity, which is exactly why the choice needs to be made deliberately.

When you read the table, look at the second column and the third together. The second column tells you which cost leaves your shelves. The third tells you what that means for profit in a year when prices are climbing.

How to choose one method

You are choosing one method to apply consistently, not picking the most flattering number each period. Work through these questions before you decide.

1. Start with the rules. Confirm which methods your accounting framework and tax rules allow for your business. If only one is allowed, the choice is already made.

2. Match the method to how goods move. If each batch is kept and sold in order, FIFO fits naturally. If identical items are poured, stacked or blended together, weighted average is often easier to apply honestly. LIFO fits well only when your reasons for it are clear and documented.

3. Look at your price history. If your supplier prices hardly move, the method will make little difference, and simplicity should win. If prices swing up and down, the method can change your profit, your tax and the value of your stock, so the choice deserves more thought.

4. Be honest about your records. FIFO and LIFO need batch-level tracking, with dates and unit costs for every purchase and a clear link from each sale to its batch. Weighted average needs a running total and a recalculated average after every purchase. Pick the method your team can keep up with every month, not just in a good month.

5. Think about who reads your numbers. Lenders and investors will judge your figures too. If outside readers matter to you, weigh that heavily.

6. Plan for consistency. Changing methods later may need a sound reason, documentation and sometimes disclosure, and it makes year-to-year comparisons harder. Choose a method you expect to keep for a long time, and write down why you chose it.

Whichever method you pick, record it in your written accounting policies so the next bookkeeper, auditor or adviser can see what was done and why.

Practical habits for bookkeepers

Every invoice you send for stock should trace back to a cost, so your method has to work at the level of individual sales. These habits make that possible. Start with the first two, because the rest depend on them.

• Record each purchase in full. Keep the date, quantity, unit cost, supplier and invoice reference for every batch. Batch-level methods depend on this detail, and it helps even if you use weighted average. For related guidance, see electronic invoice records.

• Link each sale to its cost. For FIFO or LIFO, note which batch each sold unit came from. For weighted average, record the average in effect at the time of the sale.

• Decide how extra costs are treated. Shipping, duty and handling charges can change the cost of stock. Decide whether they are included in stock cost, and apply that choice to every purchase in the same way.

• Handle returns consistently. When a customer returns goods, or you return goods to a supplier, bring the stock and its cost back into the records in a way that matches your method.

• Count and reconcile. Compare physical counts with your records at least at period end. Differences often point to recording errors, theft or damage, and they distort cost of sales if left alone. For a related check, see reconcile invoice payments with your bank.

Confirm the setting matches your written policy before you run reports, and check it again after any upgrade. The same Zoho help page warns about large catalogues: "Note: If your organisation has more than 1,000 items, you cannot view this report within Zoho Inventory - export it to view it." If your item list is long, plan for an export step and check the totals in the exported file.

Mistakes to avoid

A few errors come up again and again when small businesses handle inventory costs. Watch for these in your own books.

Switching methods to manage profit is the most serious. A change made because one year looks weak is hard to defend, and it undermines the comparison between periods that the method is meant to support.

Applying different methods to similar items without a documented reason is another common problem. If two products are sold and stored the same way, they should usually follow the same method. If they do not, write down the difference and why it exists.

Forgetting to update the average after a purchase is an easy mistake under weighted average. Each new delivery changes the average, so a stale figure will carry through every invoice until someone notices.

Leaving returns, credit notes and partial shipments out of the stock records can quietly distort the numbers. Treat each of them as a movement that changes either the quantity on hand or the cost of sales, and record it the same way every time.

Mixing methods within one year is a quieter error. Some people apply FIFO in the warehouse software and LIFO in the spreadsheet that feeds the accounts. When the two disagree, nobody can say which figure is right, so pick one source of truth and reconcile against it.

Final thoughts

FIFO, LIFO and weighted average each answer the same question in a different way: which purchase cost goes against this sale? FIFO follows the oldest stock, LIFO follows the newest and weighted average blends everything together. None of them is a magic route to a better result. Each one tells a particular story about your costs, and that story shapes your profit, your stock value and the tax you may owe.

Start this week by confirming which methods are allowed for your business. Then choose the one that fits how your goods move, how your prices behave and how well your records can support it. Write the choice down, apply it the same way every period and review it if your business changes. For the items you invoice, that steady approach will do more for the reliability of your numbers than any single clever choice.