Amazon FBA Inventory Weeks of Cover Calculator
See exactly how many weeks of stock you have left — and when you'll need your next shipment.
What Are Weeks of Cover?
Weeks of cover (WOC) is a simple but powerful inventory health metric: it tells you how many weeks your current inventory will last at your current sales pace. The formula is: Weeks of Cover = Current Inventory ÷ Weekly Sales Velocity.
Maintaining the right weeks of cover is a balancing act. Too little inventory and you risk stockouts (lost sales, rank drop, Buy Box loss). Too much inventory and you're paying unnecessary FBA storage fees, tying up capital, and risking aged inventory surcharges if products don't sell fast enough.
Target Weeks of Cover by Situation
- 4–6 weeks: Healthy range for most products with reliable domestic suppliers
- 6–10 weeks: Recommended buffer for overseas suppliers with 30–45 day lead times
- 10–14 weeks: High-velocity products approaching Q4 may benefit from extra buffer
- Under 3 weeks: Reorder immediately — you may not have enough time for a standard replenishment cycle
- Over 16 weeks: Risk of aged inventory surcharges — consider promotions to accelerate sell-through
The Relationship Between WOC and Reorder Point
Weeks of cover tells you where you are today. The reorder point calculator tells you when to act. Together, they give you a complete picture of your inventory health. When your WOC falls to a level that matches your lead time plus safety stock, it's time to reorder.
Frequently Asked Questions
Where do I find my weekly sales velocity in Seller Central?
Go to Seller Central → Reports → Business Reports → Sales and Traffic. You can also see units ordered per day/week on the ASIN-level detail report. Alternatively, the FBA Inventory Health report shows 30-day and 90-day average daily sales you can multiply by 7 for weekly velocity.
How does seasonality affect weeks of cover targets?
During Q4 (October–December), sales velocity often spikes significantly — some products see 2–5× normal velocity. Build in extra cover going into Q4. Conversely, carrying excess inventory into Q1 means higher Q4 storage fees and risk of aged inventory going into the slower months.
What is Amazon's Inventory Performance Index (IPI)?
The IPI score measures inventory management efficiency on a 0–1000 scale. Scores below 400 can result in Amazon restricting how much inventory you can send to FBA. Maintaining healthy weeks of cover (not too high, not too low), keeping sell-through rates strong, and fixing stranded inventory all contribute to a higher IPI.
What should I do if I calculate a stockout gap?
If the calculator shows your shipment arrives after you'll stock out, you have a few options: (1) place a smaller emergency air freight order to bridge the gap, (2) create an FBM backup listing from home stock, (3) consider whether raising your price temporarily to slow sales velocity will help bridge the gap until inventory arrives.
Powered by HumanCalculations — free online calculators