Days of Supply vs Days of Inventory on Amazon FBA
Days of supply vs days of inventory: what each measures, how to calculate them, and which one tells an Amazon FBA seller when to reorder.
Co-founder & CTO, Inventory Hero
Frequently Asked Questions
- What is the difference between days of supply and days of inventory?
- Days of supply looks forward: it divides current stock by sales velocity to estimate how many days until you run out. Days of inventory looks backward: it measures how many days your average inventory took to sell over a past period. One is for restock timing; the other is for efficiency and accounting.
- How do you calculate days of supply?
- Divide your current available units by your daily sales velocity. If you have 600 units and sell 20 a day, you have 30 days of supply. Compare that number to your total lead time to know whether there is still time to reorder before you run out.
- Which metric should I use to decide when to reorder?
Written by
T. Brian Jones
Co-founder & CTO, Inventory Hero
T. Brian Jones is co-founder and CTO of Inventory Hero. He leads the engineering behind its Amazon data pipeline, demand forecasting, and the AI platform that lets sellers talk to their live inventory, sales, and supplier data in plain language.
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