Days of inventory on hand is a comforting number.
By adamweiler1 · September 8, 2026 · Curated by George's Blog
Days of inventory on hand is a comforting number.
It feels like control. You've got 26 days of stock. You're covered.
Except... what if resellers owned the buy box for 70% of those days?
Your velocity data is lying to you.
If your buy box percentage was 30% over the last 30 days, your sales weren't really yours. Resellers were capturing a huge chunk of demand. Your "days of inventory" calculation is built on distorted sales data.
And now that your buy box percentage is climbing back up? You're actually undersupplied. You just don't know it yet.
This is one of the most expensive blind spots on Amazon.
Here's the two-number check every brand should run weekly:
1️⃣ Trailing buy box % (last 30 days) — what portion of sales were actually yours over a full cycle
2️⃣ Recent buy box % (last 7 days) — where things are heading right now
Then read the relationship:
→ Trailing low, recent high = your velocity is accelerating. You're likely undersupplied. Order more.
→ Trailing high, recent low = resellers are cutting in. True demand may be higher than your sell-through suggests. Factor that in before you cut an order.
→ Both low = reseller problem that needs a strategy conversation, not just a reorder.
Inventory decisions made without buy box data are just guesses dressed up in spreadsheets.
The brands getting this right are looking at both numbers side by side every week, not just checking days on hand and moving on.
Are you factoring buy box percentage into your replenishment decisions... or just going off units sold?