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Business

Inventory Days Calculator.

Calculates how many days, on average, your current inventory will last based on your inventory value and cost of goods sold.

Results update live as you type.
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Your inputs

How it works

  1. 1

    Enter your current inventory value (cost of inventory on hand).

  2. 2

    Enter your annual cost of goods sold (COGS).

  3. 3

    Divide inventory value by daily COGS (annual COGS ÷ 365).

  4. 4

    The result is the average number of days your inventory will last.

inventory_value / (cogs / 365)

Frequently asked questions

What is a good inventory days number?

It varies by industry. Retail often targets 30-60 days, while manufacturing may have longer cycles. Compare to your industry average.

How can I reduce my inventory days?

Improve demand forecasting, negotiate faster supplier lead times, and identify slow-moving items to discount or discontinue.

What is the difference between inventory days and inventory turnover?

Inventory days shows how long inventory sits (in days), while turnover shows how many times inventory is sold and replaced in a year. They are inversely related.

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Inventory Days

0days

Inventory Turnover0times/year
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Estimate for general guidance only — verify important decisions with an appropriate professional.

How it works

Calculates how many days, on average, your current inventory will last based on your inventory value and cost of goods sold.

  1. Enter your current inventory value (cost of inventory on hand).
  2. Enter your annual cost of goods sold (COGS).
  3. Divide inventory value by daily COGS (annual COGS ÷ 365).
  4. The result is the average number of days your inventory will last.

Formulas

The math behind this calculator, written out so you can verify the result.

Inventory Days

Inventory Days = (Inventory Value / COGS) × 365

This formula converts the ratio of inventory to annual cost of goods sold into a daily measure.

Example:

Input: Inventory = $50,000, COGS = $300,000

Calculation: (50,000 / 300,000) × 365

Result: ≈ 60.8 days

Inventory Turnover

Inventory Turnover = COGS / Inventory Value

This shows how many times per year the company sells and replaces its inventory.

Example:

Input: COGS = $300,000, Inventory = $50,000

Calculation: 300,000 / 50,000

Result: 6 times per year

Real-world use cases

Where this calculation shows up in everyday life.

Monitor stock levels

Track whether you are overstocking or understocking relative to sales.

Example: If inventory days rise, you may be holding too much stock.

Cash flow planning

Understand how much cash is tied up in inventory and for how long.

Example: Longer inventory days means more cash locked in unsold goods.

Benchmark performance

Compare your inventory efficiency to industry standards or competitors.

Example: Aim to be within the typical range for your sector.

Tips and common mistakes

Tips

  • Use average inventory value over a period for more accuracy.
  • Ensure COGS matches the same period as your inventory value.
  • Seasonal businesses should calculate inventory days for each season separately.
  • Regularly review slow-moving items to avoid obsolescence.

Common Mistakes to Avoid

  • Using sales revenue instead of COGS – this overstates inventory days.
  • Mixing monthly inventory with annual COGS without adjusting.
  • Ignoring seasonal fluctuations when interpreting the result.

Assumptions and limitations

  • Use the stated inputs and units.
  • Results are estimates for planning and education.
  • Check measurements and source data before making an important decision.