What is a kardex?

If you have spent time in a warehouse, a wholesale depot or the back office of a store in Latin America, you have almost certainly heard the word kardex. People pronounce it "CAR-dex", keep it in folders, argue about it at stock-taking time and hand it to accountants at the end of every month. The name sounds like a brand or a piece of software, but the kardex is older than most of the businesses that use it. It is a record — kept on paper cards for decades and now usually inside a computer — that shows, movement by movement, exactly what happened to each product you sell: how many units came in, how many went out and how many are left. If you are reading this in English, you may have met the word through a Latin American supplier, a franchise manual, an import-export report or an accounting file. This article explains what a kardex is, why companies insist on keeping one, what its columns look like, how it connects to the cost of goods sold and to perpetual inventory, and whether you still need one when software can do the math for you. By the end, you will not only understand the term: you will know how to read one and even how to build one.

A simple definition of a kardex

A kardex is an inventory control record — originally a physical card, today usually an electronic register — that tracks every movement of a single product. Each entry that adds stock (purchases, customer returns, production, positive adjustments) and each exit that removes stock (sales, damage, returns to the supplier, negative adjustments) is written in chronological order, followed by the balance remaining after that movement. Many kardex records go further and register unit costs and values, so the same sheet that controls quantities also feeds the accounting books. The essential idea is order through detail. A shop with five hundred products does not manage one giant list; it keeps five hundred kardex records, one per product, each acting as a chronological diary of that item's life. Because movements are registered the moment they happen, the kardex is also the basic working tool of the perpetual inventory system, in which the recorded stock is supposed to match the physical stock at all times, not only after an annual count.

Where does the word "kardex" come from?

Kardex began as a brand name, not as an accounting term. In the early twentieth century, the Kardex Company — later absorbed into Remington Rand — sold filing cabinets of "visible" cards designed to store and update records quickly by sliding a new card into a labeled pocket. The system became so popular that in Latin America the brand name turned into a common noun: any card that controlled stock came to be called a kardex, the way people say "hoover" for any vacuum cleaner or "kleenex" for any tissue. This history also explains why you will see different spellings. Kardex with a K is the most common form in Spanish- and Portuguese-speaking markets. Cardex with a C appears too, as a simplified variant. In plain English, the same object is usually called an inventory card, a stock card, a stock ledger card or a perpetual inventory record. When a supplier in Mexico, Colombia or Peru tells you they will send you "el kardex", they are offering exactly that: the movement history and the current balance of a product.

Why a kardex matters

Without a kardex, the only way to know what you have is to count everything, and between counts you operate on guesses. With one, several practical problems disappear at once:

You know the balance without counting. The record answers "how many do I have?" in seconds, for any product, for today or for any date in the past.
You can plan purchases. When the balance of an item approaches its minimum level, the kardex shows how fast that product has been moving, which supports the reorder decision with facts instead of feelings.
You detect losses and errors. Comparing the physical count with the kardex balance reveals shrinkage from theft, breakage, misplacement or poor record keeping — and even helps locate the moment it happened.
You can value your inventory. A valued kardex gives the total worth of your stock on any date, which is needed for financial statements, insurance and credit applications.
You support your accounting and taxes. In several Latin American countries, the cost of goods sold declared to the tax authority or shown to an auditor must be traceable to supporting records, and the kardex is the standard piece of evidence.

For all of these reasons, the kardex is not bureaucracy for its own sake: it is the bridge between the warehouse floor and the profit-and-loss statement.

The typical columns of a kardex

Kardex designs vary by country, software and personal preference, but almost all share the same anatomy. At the top, a header identifies the product: code, description, unit of measure, storage location, minimum and maximum stock, main supplier and the period covered. Below it, the movement table usually includes:

Date — when the movement occurred.
Document number — the purchase invoice, sales invoice, delivery note or adjustment form that supports the movement.
Description or type of movement — purchase, sale, return, damage, adjustment.
Entries — quantity, unit cost and total value of what came in.
Exits — quantity, unit cost and total value of what went out; for a sale, that total is the cost of the goods sold.
Balance — quantity, unit cost and total value remaining after the movement.

There is one detail worth underlining: in a proper kardex, the entry and exit columns are always valued at cost, never at selling price. The selling price appears on the invoice; the kardex exists to feed the accounting books, where inventory and cost of sales are measured at cost. Confusing cost with selling price is one of the most common mistakes when someone turns a simple stock list into a real kardex.

Kardex vs inventory card vs cardex: same record, different names

Are these different things? For practical purposes, no. An inventory card, a stock card and a cardex are all names for the same kind of record, and kardex is simply the most widespread word in the Spanish- and Portuguese-speaking world. If there is one nuance worth knowing, it is that a plain bin card hung next to the shelves sometimes records only quantities, while a full kardex — the accounting kind — values every movement. When someone asks for a kardex in a business or accounting context, assume they want the valued version, quantities plus costs, because that is the one that supports financial statements and tax returns.

The kardex, the cost of goods sold and perpetual inventory

Two accounting ideas are inseparable from the kardex. The first is perpetual inventory. Under a perpetual system, the inventory balance is updated continuously, after every purchase and every sale, instead of being recalculated only when a physical count is done at the end of the period. The kardex is precisely that: a perpetual, product-by-product ledger. The second idea is the cost of goods sold (COGS). The classic formula is: COGS = beginning inventory + purchases − ending inventory. A valued kardex gives you the same result in a more direct way: each time you sell, the exit column records the cost of the units sold, and the cost of goods sold for a month is simply the sum of that column. The classic formula then works as a cross-check rather than as the only method available. The unit cost used on each line depends on the valuation method the company adopts and applies consistently: weighted average cost, the most common in Latin America and accepted by IFRS (IAS 2); FIFO, first in, first out; or specific identification for unique items. Finally, at least once a year the physical count is reconciled with the kardex, and any difference is registered as an adjustment so that the record and reality agree again.

A kardex in practice: a simple example

Suppose you sell a stainless steel water bottle and you use the weighted average cost method. On June 1 your kardex opens with 10 bottles purchased at $10.00 each. Every movement is then added to the table, line by line:

Date	Movement	Units in	Units out	Balance	Unit cost	Value in	Value out	Balance value
Jun 1	Opening balance	—	—	10	$10.00	—	—	$100.00
Jun 3	Purchase, invoice 1042	20	—	30	$10.00	$200.00	—	$300.00
Jun 7	Sale, invoice 0051	—	15	15	$10.00	—	$150.00	$150.00
Jun 12	Purchase, invoice 1067	10	—	25	$13.00	$130.00	—	$280.00
Jun 18	Sale, invoice 0087	—	10	15	$11.20	—	$112.00	$168.00
Jun 30	Ending balance	—	—	15	$11.20	—	—	$168.00

Let us walk through the arithmetic. On June 3 the purchase of 20 bottles at $10.00 leaves 30 units worth $300.00, still $10.00 each. The June 7 sale takes 15 units out at that same cost, $150.00, and leaves 15 units valued at $150.00. On June 12 a new purchase arrives at a higher price: 10 units at $13.00 add $130.00, so the balance becomes 25 units worth $280.00. From that moment the unit cost is recalculated as a weighted average: $280.00 divided by 25 equals $11.20. The June 18 sale therefore exits 10 units at $11.20 each, or $112.00, leaving 15 units valued at $168.00. The cost of goods sold for June is the sum of the two exits: $150.00 + $112.00 = $262.00. Now check with the classic formula: beginning inventory $100.00, plus purchases of $330.00 ($200.00 + $130.00), minus COGS of $262.00, equals $168.00 — exactly the closing balance on June 30. That internal consistency is what makes a kardex trustworthy: if the arithmetic does not close, something was misregistered, and the record has done its job by pointing at the problem.

Manual kardex vs digital kardex

For most of its history, the kardex was a paper card filed in a cabinet, updated with a pen. That manual version is still alive in thousands of small shops, and it has honest advantages: it costs almost nothing, needs no electricity, no training and no internet, and it can survive for years if it is stored carefully. But it also has well-known weaknesses: handwriting that becomes illegible, arithmetic errors that nobody notices, entries that only one person can make at a time, pages that get lost or burned, and cards that simply do not get updated when the owner is busy selling. Today most kardexes live in software. At the simplest level, a spreadsheet with the same columns works, although it keeps many manual risks: broken formulas, duplicated versions and cells overwritten by accident. Dedicated inventory software goes further. It updates the kardex automatically with every sale, purchase or return; applies the valuation method you chose; keeps an audit trail of who changed what; serves several users, warehouses and stores at the same time; warns you when stock reaches the minimum; and produces the valuation and cost-of-goods-sold reports that accounting and tax authorities ask for. For a company that must present its kardex to an auditor, exporting a clean, dated report takes one click instead of an afternoon with a calculator. In the end, the debate between paper and screen matters less than a simple discipline: register every movement at the moment it happens. An updated kardex protects your inventory, your purchases and your profits; an abandoned one is just paperwork. If you want to see how an automatic kardex behaves in a real business, take a look at Kardex Tauro, an online inventory system that builds and updates the kardex of every product with each sale or purchase — the modern version of that old card, without the pen.

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