Inventory Turnover: Shopify Reorder Math Guide

What Inventory Turnover Actually Tells You

Inventory turnover ratio = cost of goods sold over a period divided by average inventory value in that period. A turnover of 6 means you sold through your average inventory six times per year — roughly every two months. Higher turnover means cash cycles faster; lower turnover means cash sits on shelves.

Benchmarks vary wildly by category: fast fashion might turn 8–12x yearly while furniture turns 2–4x. The number to beat is your own trend line — turnover declining quarter over quarter signals overbuying or slowing demand long before it shows up as a cash crisis.

Turnover connects directly to profit. Every unit gathering dust ties up the cash you spent acquiring it plus storage costs, while every stockout on a bestseller forfeits margin you already paid to earn via ads. The reorder math below balances both risks.

The Reorder Point Formula, Step by Step

1. Calculate average daily sales per SKU: units sold in the last 30–90 days divided by days. Use 90 days for stable products, 30 for trending ones.
2. Measure supplier lead time in days: from purchase order to goods ready to sell. Include production, freight, and receiving.
3. Compute base reorder point: daily sales × lead time days. This is the inventory level that exactly covers demand while you wait.
4. Add safety stock (below) to cover demand spikes and late deliveries.
5. Set reorder quantity to cover the next order cycle: daily sales × days between orders, plus a growth buffer.

SKU example	Daily sales	Lead time	Safety stock	Reorder point
Bestseller A	20 units	21 days	140 units	560 units
Steady B	5 units	14 days	25 units	95 units
Slow C	1 unit	30 days	10 units	40 units

Illustrative numbers. Safety stock here assumes roughly one week of demand coverage — adjust using the method below based on your variability.

Safety Stock Without the Statistics PhD

The textbook formula multiplies demand variability by lead-time variability by a service-level factor. In practice, most Shopify stores can use a simpler rule: safety stock = average daily sales × (maximum lead time − average lead time) + a demand-spike buffer of 20–50% for promotional periods.

Calibrate by pain: if you stocked out twice last quarter, your safety stock is too thin — raise it. If your warehouse is full of six-month-old inventory, it's too fat. Review safety stock quarterly per SKU; set-and-forget is how dead stock accumulates.

Dead Stock vs. Stockouts: Picking Your Poison

Every inventory decision trades off two costs. Stockouts cost you the margin on lost sales plus the ad spend that drove the traffic — often the larger number for paid-traffic stores. Dead stock costs you tied-up capital, storage fees, and eventual clearance discounts.

• For bestsellers: err toward overstock. The cost of a stockout on a proven winner almost always exceeds the carrying cost of extra units.
• For unproven SKUs: err toward understock. Test with small batches; reorder winners aggressively.
• For seasonal items: set a hard sell-through date and mark down early. Hope is not an inventory strategy.
• For slow movers: bundle them with bestsellers or clearance them — every month they sit, they drag your turnover ratio down.

Run an ABC analysis quarterly: rank SKUs by revenue contribution. Your A-items (typically the top 20% driving ~80% of revenue) get tight reorder math and generous safety stock; C-items get minimal investment. Discipline here is what separates stores with healthy cash flow from stores with full warehouses and empty bank accounts.

Document your reorder math per SKU in a shared sheet: daily sales rate, lead time, safety stock, and reorder point. When the numbers live in someone's head, vacations and staff changes create the exact stockouts the system was built to prevent.

Putting It on Autopilot: Tools and Reviews

Manual reorder math works until it doesn't — usually around 50 SKUs or your second supplier, whichever comes first. At that point, inventory apps that sync with Shopify and apply reorder-point logic automatically pay for themselves by catching the stockout your spreadsheet missed. Look for tools that handle supplier lead-time tracking and low-stock alerts, not just quantity syncing.

Whatever system you use, institute a monthly inventory review: check turnover trend per ABC tier, flag SKUs below your stockout threshold, and identify dead stock over 90 days old for action. Thirty minutes a month prevents the two classic failures — the surprise stockout on a bestseller and the warehouse full of last season's guesses.

Tie the review to purchasing discipline: no new SKU gets added without a test-batch plan and a kill date. Every product earns its shelf space with turnover, or it leaves. That single rule does more for cash flow than any software.

Inventory decisions are profit decisions — model carrying costs and stockout losses alongside your other margins using the Shopify Profit Calculator and our Shopify net profit breakdown.