Days of Inventory Calculator

Track inventory days using average stock and costs. Detect overstock earlier and plan leaner replenishment. See coverage, velocity, and reorder insight in one place.

Enter Inventory Data

Example Data Table

This sample shows how average inventory and cost flow affect coverage days.

Item Beginning Inventory Ending Inventory COGS Period Days Average Inventory Days of Inventory
Running Shoes $50,000 $35,000 $90,000 30 $42,500 14.17
Phone Cases $18,000 $22,000 $24,000 30 $20,000 25.00
Protein Powder $70,000 $62,000 $84,000 28 $66,000 22.00

Formula Used

Average Inventory = (Beginning Inventory + Ending Inventory) ÷ 2

Daily COGS = Cost of Goods Sold ÷ Period Days

Days of Inventory = Average Inventory ÷ Daily COGS

Inventory Turnover = Cost of Goods Sold ÷ Average Inventory

Safety Stock Days = Safety Stock Value ÷ Daily COGS

Usable Inventory Days = (Average Inventory - Safety Stock Value) ÷ Daily COGS

These formulas estimate how many days your current average stock can support expected cost flow over the selected period.

How to Use This Calculator

  1. Enter the item name and your preferred currency symbol.
  2. Provide beginning and ending inventory values for the selected period.
  3. Enter cost of goods sold and the number of days in that period.
  4. Add safety stock, target coverage, and supplier lead time.
  5. Press the calculate button to show results above the form.
  6. Review coverage, turnover, reorder alert, and stock status.
  7. Use the CSV and PDF buttons to export the result summary.

FAQs

1. What does days of inventory measure?

It measures how long your average inventory can support sales activity, based on cost of goods sold over a chosen period.

2. Why is average inventory used?

Average inventory smooths opening and closing balances, giving a more stable estimate than using only one inventory value.

3. Is a higher result always better?

No. Very high inventory days may signal overstock, slow movement, tied-up cash, storage pressure, or markdown risk.

4. How is this different from inventory turnover?

Turnover shows how often inventory cycles through sales. Days of inventory converts that speed into easy-to-read time coverage.

5. Should I include safety stock?

Yes, when you reserve stock for uncertainty. It helps distinguish total coverage from the inventory truly available for normal demand.

6. Can this help with reorder timing?

Yes. Compare inventory days with lead time and safety stock coverage to spot when replenishment should begin.

7. What period should I use?

Use a period that matches your reporting cycle, such as 30, 60, 90, or 365 days, for consistent comparisons.

8. Can ecommerce businesses use this for each SKU?

Yes. It works well for individual products, categories, or full catalogs when values and costs are available.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.