At a glance
How many days your current inventory will last at the recent rate of sale. For each SKU, the card divides available units by the trailing daily sales rate to get days of cover, then averages across the catalogue (with the top sellers weighted by attention). Too few days means a stockout is coming, which kills Buy Box and burns ad spend; too many days means cash is trapped in slow stock and FBA storage fees are mounting. The sweet spot leaves enough runway to reorder and replenish before you run dry.
| What it counts | Average days of inventory cover across SKUs: available units / trailing daily sales rate, averaged across the catalogue. It estimates how long current stock will last at the recent selling pace. |
| FBA vs FBM | For FBA, available units are the sellable units in Amazon fulfilment centres (excluding reserved, inbound, and unfulfillable). For FBM, it is your own warehouse availability as synced to Amazon. The card focuses on what can actually be sold now. |
| Why an average is a starting point | A single catalogue average hides the SKUs that matter. A healthy average can sit on top of several top-20 SKUs about to stock out. Always drill into the per-SKU view for the ASINs that drive revenue. |
| Demand basis | The trailing daily sales rate is computed over a recent window. A SKU coming off a promo spike shows artificially low cover; a SKU heading into season shows artificially high cover until demand ramps. |
| Inbound / reserved units | Units inbound to FBA or reserved for pending orders are typically excluded from “available”, so cover can read lower than your total owned stock. This is intentional, it reflects sellable runway. |
| Link to stockouts and ads | Low cover on a top SKU is the leading indicator for the ASINs Stocking Out <7 Days and Ad on OOS Detected cards. |
| Reading the value | Compare against your reorder lead time. Cover comfortably above lead time is safe; cover below lead time on a top SKU means you may already be too late to avoid a gap. |
| Currency / unit | number (days) |
| Time window | RT (real-time / latest available snapshot) |
| Alert trigger | <14 days on top-20 SKUs |
| Roles | owner, operations, finance |
Calculation
Calculated automatically from your Amazon Seller Central data. See the At a glance summary above for what the metric tracks and the worked example below for a typical reading.Worked example
A pet-supplies brand on Amazon UK, FBA, snapshot 30 Apr 26, reorder lead time roughly 21 days. All numbers illustrative.| SKU (top 20) | Available units (FBA) | Trailing daily sales | Days of cover | Status vs 21-day lead time |
|---|---|---|---|---|
| Dog chews, large | 420 | 60 | 7 | Already too late, gap likely |
| Cat litter 10L | 1,800 | 90 | 20 | Reorder now |
| Puppy pads 100pk | 2,400 | 40 | 60 | Healthy |
| Grooming brush | 95 | 12 | 8 | Too late, expedite |
| Slow feeder bowl | 5,000 | 25 | 200 | Overstocked, watch storage fees |
| Top-20 average | ~19 days | Below 21-day lead time |
- The average hides two emergencies. The top-20 average of ~19 days looks borderline, but dog chews (7 days) and the grooming brush (8 days) are already below lead time. By the time stock arrives, both will have stocked out. The average is reassuring; the per-SKU view is not.
- 19 days breaches the alert. With the top-20 average under the
<14 days on top-20 SKUsline being approached and individual SKUs already under it, Vortex IQ Nerve Centre flags the at-risk SKUs. The right response is per-SKU expediting, not a blanket reorder. - The slow feeder bowl is the opposite problem. 200 days of cover means cash is trapped and FBA long-term storage fees are looming. Pair with ASINs Approaching Long-Term Storage and consider a markdown or removal.
- Lead time, not a fixed number, sets your floor. A 14-day cover is fine for a SKU with a 7-day lead time and dangerous for one with a 21-day lead time. Always read cover against the specific SKU’s replenishment lead time.
- A promo distorts the rate. If the dog chews just came off a 7-day deal, the trailing daily rate of 60 is inflated and real cover is better than it looks. Check whether the recent rate reflects normal demand before reacting.
Sibling cards merchants should reference together
Cover is a leading indicator; pair it with the consequences:| Card | Why pair it with Days of Cover (avg) |
|---|---|
| ASINs Stocking Out <7 Days | The sharp end of low cover, the SKUs about to run dry. |
| Replenishment Recommendations | Turns low cover into a reorder action list. |
| Sell-Through Rate (FBA) | The other side of the coin; high cover plus low sell-through means overstock. |
| ASINs Approaching Long-Term Storage | Excessive cover ages into long-term storage fees; this card catches it. |
| Ad Spend on Out-of-Stock ASINs | When cover hits zero, ad spend on that ASIN is wasted; this card quantifies it. |
| Stranded Inventory Value | Stock that cannot sell at all is the worst kind of trapped cover. |
Reconciling against Amazon Seller Central
Where to look in Amazon Seller Central:Seller Central → Inventory → Inventory Planning (FBA) shows days of supply and a sell-through view per SKU. The Restock Inventory tool surfaces Amazon’s own days-of-supply estimate and recommended reorder quantities, which is the closest native equivalent.For raw availability, Seller Central → Inventory → Manage FBA Inventory shows available, reserved, inbound, and unfulfillable units per SKU. Timing, settlement, and reporting-lag table:
| Topic | Detail |
|---|---|
| Timezone | Inventory snapshots are point-in-time rather than window-bounded, so timezone has little effect. The card reads the latest available snapshot. |
| Available vs total | Amazon’s available units exclude reserved (pending orders), inbound, and unfulfillable units. The card uses sellable availability, so it can read lower than your total owned stock. |
| Demand-window choice | Amazon’s Restock tool and the card may use different trailing windows for the sales rate. A different window changes days of cover even with identical stock. |
| Refresh lag | FBA inventory counts update frequently but not instantly; a large receipt or a sales burst can take a refresh cycle to reflect. |
| Reason | Direction | Why |
|---|---|---|
| Sales-rate window | Either | Amazon’s days-of-supply may use a different trailing window than the card; a longer window smooths spikes, a shorter one reacts faster. |
| Inbound treatment | Either | Whether inbound units are counted toward cover differs between views; the card focuses on currently sellable stock. |
| Seasonality adjustment | Either | Amazon’s Restock estimates can apply forecast adjustments; the card uses recent realised demand unless configured otherwise. |
| SKU aggregation | Either | The card’s average weights the top sellers; a flat SKU list in Seller Central will not match the weighted average. |
| Card | Expected relationship | What causes legitimate divergence |
|---|---|---|
shopify.total_revenue | If FBM stock is shared with a DTC store, DTC sales draw down the same pool, shortening real cover. | If inventory is not synced, Amazon cover can look healthy while shared stock is actually depleting via DTC orders. |
ebay.out-of-stock-listings | Cross-marketplace inventory pressure. A shared FBM pool sold on both Amazon and eBay drains faster than either channel’s cover suggests. | Each marketplace reads its own availability; only a synced pool reflects total drawdown. |
Known limitations / merchant FAQs
The average looks fine but I still stocked out. Why? Because an average hides the SKUs that matter. A healthy catalogue average can sit on top of several top-revenue SKUs about to run dry. Always drill into the per-SKU view and read cover against each SKU’s reorder lead time. Why is my cover lower than my total stock suggests? The card uses sellable (available) units, which exclude reserved, inbound, and unfulfillable inventory. Units on a boat to the fulfilment centre do not count toward cover until they are received and sellable. A SKU just came off a promotion and its cover collapsed. Is it real? Often not. The trailing daily sales rate is inflated by the promo spike, so cover reads artificially low. Wait for demand to normalise, or check whether the recent rate reflects steady-state demand before expediting a reorder. What is a safe number of days of cover? There is no universal answer; it depends on your reorder lead time. Cover should comfortably exceed lead time plus a safety buffer. A 14-day cover is fine with a 7-day lead time and dangerous with a 21-day lead time. Can I change the alert threshold? Yes. The<14 days on top-20 SKUs default is configurable per profile in the Sensitivity tab. Set it to your typical reorder lead time plus a buffer so the alert fires while there is still time to act.