XBKit·Amazon

Inventory Turnover Calculator

Calculate how fast your inventory sells. High turnover means lean cash flow; too slow risks long-term storage fees.

Inventory Data

Amazon Storage Fees

Jan–Sep: $0.78/cu ft/mo (standard)

Oct–Dec: $2.40/cu ft/mo (Q4 peak)

Long-term (>365 days): $6.90/cu ft/mo

Formula
Days to Sell=30÷Monthly Turnover Rate
  • Monthly Turnover = Sales ÷ Avg Inventory
  • Ideal DSI (Amazon FBA)14 – 45 days
  • Long-term storage risk> 365 days
  • Stockout risk< 7 days

How to Use

  1. 1

    Enter current inventory units

    Input the number of units currently in stock (at FBA warehouse or in your own storage).

  2. 2

    Enter daily or monthly sales velocity

    Input how many units you sell per day or per month based on your recent sales data.

  3. 3

    Review days of supply

    See how many days until your current stock runs out at the current sales rate. This is your Days of Supply (DOS).

  4. 4

    Check turnover rate

    Review your annual inventory turnover ratio. Higher is better — low turnover means cash is tied up in slow-moving inventory.

Frequently Asked Questions

What is inventory turnover rate?

Inventory turnover measures how many times you sell through your entire inventory in a year. Turnover = Annual Sales ÷ Average Inventory Value. A rate of 6–12 is healthy for most e-commerce businesses; below 4 suggests overstock.

What is Days Sales of Inventory (DSI)?

DSI (also called Days of Supply) is how many days it would take to sell all current inventory at the current sales rate. DSI = Inventory Units ÷ Daily Sales Rate. Amazon recommends keeping 30–60 days of supply to avoid stockouts and storage penalties.

When does Amazon charge long-term storage fees?

Amazon charges aged inventory surcharges on units stored over 181 days (6 months). Items over 365 days face higher surcharges. Monitoring your Days of Supply helps you identify products at risk before fees accrue.

How do I improve a poor inventory turnover rate?

Options include: running promotions to accelerate sales, reducing your reorder quantity, removing slow-moving inventory from FBA (create a removal order), or discontinuing underperforming SKUs to free up capital.

Related Tools

Reorder Point CalculatorSafety Stock CalculatorFBA Profit Calculator