Serial Number Inventory Tracking: A Finance Control

For a retailer, inventory is usually the largest asset and cost of goods sold the largest expense. Yet in many small shops stock is counted once a year and any difference becomes "shrinkage". That hides whether the stock figure is real, whether the margin is real, and whether anyone is using the gap between the two.

Which items need serial, lot or quantity tracking?

Not every item needs the same tracking. It helps to think of three levels.

• Quantity only. Cables, cases, chargers. You know you have 140 of an item; you do not need to know which 140.
• Lot or batch. Items made or received together, sharing a production date, a supplier delivery or an expiry date. Batteries, adhesive screen protectors, prepaid vouchers, cosmetics, food. If there is a recall or an expiry, you need to know which lot is affected.
• Serial. Each unit is unique: phones with IMEIs, laptops, appliances, anything with a manufacturer warranty. You need to know exactly which unit you bought, from whom, at what cost, and to whom you sold it.

The tracking level should follow the money and the risk, not the warehouse's convenience. A 600 phone deserves a serial. A 3 cable does not.

Why is inventory tracking an accounting question?

Valuation

Accounting standards require inventory to be measured at the lower of cost and net realisable value (IAS 2; Section 13 of IFRS for SMEs). Cost is assigned using a permitted formula, typically first-in, first-out or weighted average. Specific identification of individual costs is required in two cases only: items that are not ordinarily interchangeable, and goods or services produced and segregated for specific projects (IAS 2.23). Identical phones of one model can properly be costed at weighted average, but a serial number still lets you trace every unit from the supplier's delivery to the customer's receipt.

Expiry dates feed straight into net realisable value. A lot of vouchers or batteries that expires next month, and that you cannot sell in time, is worth less than its cost. Without lot and expiry data, that write-down is a guess at year end. With it, it is a report.

Margin

If the cost attached to a sale is wrong, the margin is wrong. When stock is tracked only by quantity and the count is out, every sale is costed against a pool that does not match reality. Serial tracking ties each sale to the cost of that specific unit or to a correctly maintained average.

Fraud and leakage

Shrinkage is not one thing. It is theft, unrecorded sales, receiving errors, supplier short-shipments, damaged goods quietly binned and returns that were never genuine. Serial and lot data let you separate them, because each unit has a history.

How do serial numbers explain inventory shrinkage? A worked example

A phone shop's ledger shows 42 units of a popular model at a weighted-average cost of 410 each, a stock value of 17,220. The month-end count finds 40.

Without serial tracking, the conversation is short: two phones are missing, 820 is written off to shrinkage, and nobody knows why.

With serial tracking, the shop compares the IMEIs on the shelf against the IMEIs the system says are in stock. Two serials are unaccounted for. Looking them up:

• Serial ending 1123 appears on a handwritten receipt from a day when the till was offline. The sale, at 520, was never entered. This is not shrinkage. It is an unrecorded sale, and the cash should be in the drawer or the bank. Record the sale; check the cash box for that day.
• Serial ending 4456 has no record anywhere after it was received. This is a genuine loss, and it is now a specific one: received on a known date, from a known delivery, last seen by a known shift.

The accounting result is different too. Instead of an 820 shrinkage expense, the shop books a sale of 520 with a cost of 410, and a shrinkage loss of 410. The margin report is right, the cash count can be checked, and the loss has a starting point for investigation.

Now consider returns. A customer brings back a phone under the shop's 14-day return policy. The returned unit's IMEI does not match the one sold on the receipt. Without serial tracking the swap goes unnoticed and the shop takes back a faulty or older device at full price. With it, the till refuses the match and a person decides. (If the original sale itself was wrong, it is corrected by reversal, not deletion, and the serial history shows the unit going out, back and out again.)

How do expiry dates change the inventory write-down?

The same shop sells prepaid top-up vouchers bought in lots. A lot of 60 vouchers, cost 9 each, expires at the end of next month. Recent sales are about 25 a month.

If expiry is tracked by lot, the system can show this lot at month end with its expiry date. On current sales, about 35 vouchers will expire unsold. If expired vouchers are worthless and the supplier will not take them back, net realisable value for that portion is nil, and a write-down of 35 × 9 = 315 is appropriate, unless the shop acts first: move them to the front, discount them, or negotiate a return. Either way, the decision is made a month early, not discovered after the fact.

What does Sunrise 2027 mean for 2D barcodes?

Today most retail barcodes carry only a product number. GS1, the organisation behind retail barcodes, is leading an industry effort known as Sunrise 2027, with the goal that retail point-of-sale systems can read 2D barcodes (such as QR codes and GS1 DataMatrix) by the end of 2027. It is voluntary and led by industry rather than regulators, and 1D barcodes are not being banned. But a 2D code can carry the lot, serial number and expiry date alongside the product number, and the GS1 Digital Link standard lets that information be encoded as a web address.

For a small retailer, the practical effect over the next few years is that suppliers will increasingly deliver goods whose barcodes already carry lot, serial and expiry. Whether your books benefit depends on whether your system can capture that data at receipt and carry it through to the sale.

How do you track serials without drowning in data?

• Capture at receipt, not at sale. Serials and lots should enter the system when goods arrive, against the supplier's delivery. That is when you can still dispute a short delivery.
• Make the sale prove the unit. At the till, scanning the serial should be required for serial-tracked items. A sale without a serial is an exception, not a shortcut.
• Count by cycle. Count high-value serialised stock weekly in small groups rather than everything once a year.
• Reconcile value as well as quantity. The stock report and the inventory account in the ledger should agree. If they do not, find out why before the year end.

How this looks in GrowMore

In GrowMore every serial-tracked unit is registered on the purchase: its barcode is scanned, or generated when the purchase posts, and printed as a label. A lot carries its units and its expiry date. A sale or a return names the unit, cost follows the moving weighted average recomputed on every receipt, a stock count posts its difference, and the server checks the inventory account against the whole stock. Lots and serial numbers are part of the Basic plan and up. The features page lists the rest.

What to do this month

• Classify your top 50 items by value into quantity-only, lot, or serial tracking.
• For every serial-tracked line, confirm serials are captured on receipt from the supplier.
• Run one cycle count of your most valuable model and reconcile it by serial, not just by number.
• List lots expiring in the next 60 days and decide: sell, return or write down.
• Check that the inventory account in the ledger equals the stock valuation report.
• Ask your main suppliers whether their labels will carry 2D codes with lot and serial data, and when.

Frequently asked questions

Do I need serial numbers if I already use weighted average cost?

Yes. They answer different questions. The cost formula decides what each sale costs; the serial proves which unit was bought, sold or returned. Identical phones of one model can be costed at weighted average while every IMEI is still traced.

What is the journal entry for inventory shrinkage?

Debit a stock loss or shrinkage expense and credit inventory, at cost. In the example above, only one phone is a genuine loss, so the entry is 410, not 820.

What is net realisable value?

The estimated selling price in the ordinary course of business, less the costs to complete and sell. When it falls below cost, the stock is written down to it.

Read next

Slow stock ties up cash. Our 13-week cash flow forecast shows how pausing slow lines keeps money in the account when a big payment is coming.

Sources

1. IASB, IAS 2 Inventories (cost formulas; lower of cost and net realisable value). https://www.ifrs.org/issued-standards/list-of-standards/ias-2-inventories/
2. IASB, IFRS for SMEs Accounting Standard, third edition (February 2025, effective 1 January 2027), Section 13 Inventories. https://www.ifrs.org/content/ifrs/home/news-and-events/news/2025/02/iasb-issues-major-update-smes-accounting-standard
3. GS1 US, Sunrise 2027 (industry goal for retail point-of-sale systems to read 2D barcodes by the end of 2027). https://www.gs1us.org/industries-and-insights/by-topic/sunrise-2027
4. GS1, GS1 Digital Link standard (encoding GTIN, batch/lot, serial and expiry in a web-resolvable identifier). https://www.gs1.org/standards/gs1-digital-link