How to Stay Ahead of Inventory Swings in a Volatile Market

Inventory volatility costs US retailers over $1.75 trillion a year in stockouts and overstock combined. For growing brands shipping into fulfillment centers, the pain hits twice: lost sales from empty shelves, and locked-up capital from unsold goods. Here are seven metrics the best operations managers watch.

1. Days of Supply (DOS)

DOS = On-hand inventory / Average daily unit sales. Set a target DOS by SKU class (A, B, C) and trigger reorder when actual DOS drops below the target. A-items might run at 21 DOS, C-items at 60.

2. Sell-Through Rate

Units sold / Units received over the same period. A sell-through below your target by week 4 of a season signals a markdown decision; above target signals a reorder.

3. Lead Time Variability

Average lead time matters, but variance matters more. A supplier with a 25-day lead time and 2-day standard deviation is easier to plan than one at 20 days with 10-day standard deviation. Track both.

"If you only measure the mean, you'll be surprised by the tails. Safety stock exists because of variance, not averages."

4. Forecast Accuracy (WMAPE)

Weighted Mean Absolute Percent Error, weighted by unit volume. Measure accuracy at the SKU-week level; a company-wide WMAPE under 25% is strong, under 15% is best-in-class.

5. In-Stock Rate

Percent of SKUs available on your channels at any point in time. Target 98%+ on A-items and 95%+ overall. Below those, you're leaking revenue.

6. Weeks of Supply (WOS)

Similar to DOS but at weekly granularity for seasonal businesses. Pair with forward demand so you can distinguish real excess from pre-peak build.

7. Receive-to-Available Lag

Hours (or days) between a shipment arriving at the DC and inventory being available to sell. Under 24 hours is standard; under 4 hours is best-in-class and requires scan-at-dock and automated putaway rules.

Build a Simple Dashboard

You don't need Snowflake and Looker. Start with a weekly Excel or Sheets report that shows DOS, forecast vs actual, in-stock rate and lead time variability by top-50 SKU. Review it every Monday morning for 30 minutes and you'll outperform most teams in your category.