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Days sales of inventory tells you how many days your stock sits on the shelf before it sells. It’s often shortened to DSI. You calculate it by dividing average inventory by cost of goods sold, then multiplying by 365.
A low number means stock moves quickly and cash keeps circulating. A high number means your money is sitting still, wrapped up in products nobody has bought yet.
Every unit sitting in your warehouse started as cash. You spent that cash, and you don’t get it back until someone buys the product. DSI puts a number of days on that waiting period.
The calculation is short. Take your average inventory value and divide it by your cost of goods sold for the period. Then multiply the result by the number of days in that period.
Use cost of goods sold rather than revenue. Inventory sits on your books at cost, so comparing it to a retail-price figure would understate the days badly.
Average inventory means the start-of-period value plus the end-of-period value, divided by two. That smoothing matters for seasonal stores, because a single snapshot can be wildly unrepresentative.
Plenty of inventory metrics give you a multiple. DSI gives you a unit everyone in the business already understands.
Think of it like the fuel gauge in a car showing range instead of litres. “Two hundred kilometres left” is instantly actionable. “Thirty litres” needs a second calculation before it means anything.
That translation is why DSI travels well outside finance. A warehouse manager, a buyer, and a founder can all act on “we’re holding 95 days of stock”. Nobody needs to convert anything first.
There’s no universal target, and anyone who quotes one is guessing. Your category sets the range.
The gap between retail types is stark. General retailers carry inventory equal to roughly 8.67% of sales, whereas special-lines retailers carry more than double that at 18.76%. Perishables sit far lower still, while furniture and jewellery sit far higher.
So compare yourself against your own history first, then against your category. A DSI that climbed from 60 to 95 days matters more than whether 95 is “good”.
Margin shapes the answer too. Retail’s average gross margin sits near 33.18%, with net margin around 5.61%. On thin net margins, tying up cash for an extra month genuinely hurts.
DSI is one leg of a bigger measure called the cash conversion cycle. That cycle tracks how long cash stays trapped between paying a supplier and collecting from a customer.
For most online stores, DSI is the longest leg by far. Card payments settle in days, so inventory is where the money actually sits.
As a result, shaving DSI is often the cheapest way to free up working capital. It costs nothing in fees and requires no lender.
Just remember the metric ignores landed cost nuances and storage fees. Two stores with identical DSI can have very different holding costs.
DSI rarely climbs because of one bad decision. It creeps up through a handful of ordinary habits.
That last one is worth flagging. Measure DSI at consistent points in the year, otherwise you’ll chase seasonal noise instead of real problems.
Some stores fight this with a just-in-time inventory approach. It cuts DSI hard, though it also removes your buffer when a supplier slips.
Imagine a WooCommerce store called Alder Lane Home, selling lamps and small furniture. It’s a special-lines retailer, so it sits at the stock-heavy end of the scale.
Alder Lane does $1,000,000 in annual sales. Using the special-lines benchmark of 18.76% of sales, average inventory works out to about $187,600.
Now apply the retail gross margin benchmark of 33.18%. That leaves cost of goods sold at roughly 66.82% of sales, or $668,200 for the year.
So DSI is $187,600 divided by $668,200, multiplied by 365. That comes out at about 102 days.
Alder Lane’s cash spends roughly three and a half months as furniture before turning back into money. Every reorder pushes more cash into that queue.
On a 5.61% net margin, the whole year’s profit is about $56,100. Meanwhile, $187,600 sits in stock, which is more than three times the annual profit.
That’s why a growing store can be profitable and still run out of money. The profit is real, but it’s parked in boxes.
Alder Lane pulls its slowest 15% of SKUs and discounts them out. Then it splits reorders into smaller, more frequent batches.
They also tighten their reorder point per product rather than across the board. Fast movers keep generous safety stock, while slow movers get almost none.
Average inventory falls to $140,000, which drops DSI to about 76 days. In practice, that releases roughly $47,600 of cash without a single extra sale.
Getting that visibility takes decent tooling, though. A store this size usually needs proper WooCommerce inventory management reporting rather than a monthly spreadsheet.
Notice what didn’t change. Revenue stayed flat at $1,000,000, and no new customers arrived.
The $47,600 came purely from holding less stock for less time. That’s cash Alder Lane can now put into ads, a new product line, or simply a buffer.
There’s a limit, of course. Push DSI too low and you start missing sales you could have made. A stockout on a best-seller costs more than the cash you freed up.
So Alder Lane sets a floor of 70 days and reviews it quarterly. That keeps the buffer honest without letting stock creep back up.
These two are the same fact told two ways. Inventory turnover counts how many times you sell through your stock in a year. DSI converts that count into days.
The maths connecting them is simple. Divide 365 by your turnover and you get DSI. A turnover of 4 becomes about 91 days.
Turnover reads better in board packs and category comparisons. By contrast, DSI reads better when you’re planning purchase orders or worrying about cash.
Neither tells you which products are the problem. For that you need sell-through rate at the SKU level.
It depends entirely on what you sell. Fresh food might run under 10 days, whereas furniture or jewellery can sit past 120 and still be normal.
The useful comparison is your own trend. If DSI is creeping up while sales stay flat, you’re over-ordering regardless of what the category average says.
Always cost of goods sold. Inventory is recorded at what you paid, not what you charge.
Using revenue divides a cost figure by a retail figure. As a result, your DSI looks far better than it really is. On a gross margin of 33%, the error is roughly a third.
Not really, and that’s fine. If you never hold stock, your inventory is close to zero and so is your DSI.
The metric only earns its place once you’re buying stock upfront. For hybrid stores, calculate it on the held-stock portion alone.
Days sales of inventory turns your stock position into a number of days. Days are the unit your cash flow actually runs on. Watch the trend rather than the absolute figure, and treat any sustained rise as a warning. For most growing stores, cutting DSI is the cheapest funding available.
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