What is days of cover and how do I calculate it?
Days of cover = current on-hand inventory / average daily units sold. If you have 600 units on hand and sell 20/day, you have 30 days of cover. Set a target from lead time, demand variability, safety stock, and storage costs.
Jul 26, 2026 · 3 min read
The formula in practice
Use a 30-day rolling average of units sold, not a lifetime average. Seasonal SKUs need a shorter window (14 days) so days of cover reflects the current run rate, not last quarter.
Nova computes this per SKU and marketplace inside its FBA inventory view, so the number updates with real sales velocity.
Target ranges
45 to 75 days for stable-velocity SKUs. 30 to 45 days for launches (velocity changes fast). 60 to 90 days for slow but predictable movers. Above 120 days on a stable SKU usually means overordered.
What to watch for
Days of cover trending down 5 days per week on a top SKU means you will stock out; reorder now. Days of cover trending up on a mid-velocity SKU means demand slipped; investigate before you place the next PO.
Frequently asked questions
Should days of cover include inbound units?
Track two numbers: on-hand days of cover and total (on-hand + inbound). The gap tells you PO lead time exposure.
What is a safe minimum?
30 days for standard SKUs. Anything less risks a stockout on a demand spike or an FBA inbound delay.
How does this differ from sell-through rate?
Sell-through is backward-looking (past 90 days). Days of cover is forward-looking (how long current stock lasts).
Does Nova track this?
Yes. Nova shows days of cover per SKU inside inventory monitoring, with restock alerts before you stock out.
See this in Nova
Nova surfaces this metric per SKU so you can act before your next monthly close catches it.
Try Nova free for 14 daysRelated questions
What is a good sell-through rate on Amazon?
Amazon's sell-through rate is units shipped in the last 90 days divided by average inventory over the same period. Above 3.0 is strong (inventory turns 12x/year). 2.0 to 3.0 is healthy. Below 1.0 usually means overordered units and forecasts long-term storage fees within a quarter.
What is SKU velocity and why does it matter?
SKU velocity is the average units sold per day for a specific SKU, usually measured over a rolling 30-day window. It drives every downstream inventory decision: PO size, safety stock, days of cover targets, and IPI score. A SKU whose velocity drops 30% for two weeks is either losing search rank or facing seasonality.