Days in Inventory: Meaning, Formula, Example, and Why It Matters

Inventory can look like security, but sometimes it is cash standing still.

A manufacturer may feel safe seeing full racks, stocked raw material, and finished goods ready for dispatch. But if those items are not moving, they are not helping the business. They are occupying space, blocking money, and increasing the risk of damage, expiry, or obsolescence.

Days in Inventory helps measure this problem.

It shows how many days, on average, inventory stays in the business before it is sold or consumed. For SMEs, it is a useful working capital metric because it connects stock decisions with cash flow.

AICAN Optiwise helps manufacturers improve inventory visibility by connecting stock movement with purchase, production, sales, dispatch, and reporting.

What Is Days in Inventory?

Days in Inventory measures the average number of days inventory remains in stock before being sold or used.

It is also closely related to Days Inventory Outstanding, or DIO. In many business discussions, the terms are used similarly.

A higher number means inventory is staying longer. A lower number means inventory is moving faster.

But lower is not always automatically better. If inventory days become too low, the business may face stockouts and production delays.

The goal is balanced movement.

Days in Inventory Formula

A common formula is:

Days in Inventory = (Average Inventory / Cost of Goods Sold) x Number of Days

For annual calculation:

Days in Inventory = (Average Inventory / COGS) x 365

Average Inventory is usually:

Average Inventory = (Opening Inventory + Closing Inventory) / 2

Simple Example

Assume a manufacturer has:

• Opening inventory: Rs. 20 lakh
• Closing inventory: Rs. 30 lakh
• COGS for the year: Rs. 1.5 crore

Average inventory = (20 + 30) / 2 = Rs. 25 lakh

Days in Inventory = (25 lakh / 150 lakh) x 365

Days in Inventory = 60.8 days approximately

This means inventory stays in the business for about 61 days on average.

Why Days in Inventory Matters

Days in Inventory helps answer:

• Is stock moving fast enough?
• Is cash blocked in inventory?
• Are we overstocking?
• Are finished goods waiting too long?
• Are raw materials being bought too early?
• Are slow-moving items increasing?
• Is inventory aligned with demand?

For manufacturers, the metric is especially useful because stock exists in multiple forms: raw material, WIP, finished goods, packing material, consumables, and spares.

High Days in Inventory: What It May Mean

High days in inventory may indicate:

• Overstocking
• Weak demand planning
• Slow-moving stock
• Large minimum order quantities
• Finished goods not dispatching
• Production ahead of demand
• Dead stock
• Poor inventory review
• Long production cycle

High inventory days can create cash pressure even when sales look healthy.

Low Days in Inventory: What It May Mean

Low days in inventory may indicate efficient stock movement.

But it can also indicate risk if critical material is too low.

Possible risks:

• Stockouts
• Production stoppage
• Emergency purchases
• Missed dispatch commitments
• Higher supplier dependency

The right number depends on industry, lead time, supplier reliability, demand pattern, and production model.

Days in Inventory in Manufacturing

Manufacturers should not only look at total inventory days.

Break it down by:

• Raw material days
• WIP days
• Finished goods days
• Packing material days
• Slow-moving stock days
• Item category
• Product line
• Warehouse or location

This helps identify where inventory is actually stuck.

For example, total inventory days may be high because finished goods are waiting for dispatch, not because raw material is overstocked. The action will be different.

How to Improve Days in Inventory

Improve Demand Planning

Buy and produce closer to realistic demand.

Review Slow-Moving Stock

Identify items that have not moved for months.

Set Reorder Levels

Avoid both overbuying and late buying.

Improve Production Flow

WIP stuck between operations increases inventory days.

Dispatch Finished Goods Faster

Finished goods sitting after production delay cash recovery.

Review Supplier MOQ

Large MOQs may increase inventory days.

Track Inventory Ageing

Ageing reports reveal stock that is quietly getting stuck.

How Optiwise Helps

Optiwise by AICAN helps manufacturers track the operating data behind inventory days.

It supports visibility across:

• Inventory value and movement
• Purchase receipts
• Stock issues
• Production consumption
• Finished goods
• Dispatch status
• Slow-moving items
• Reports and dashboards

This helps owners understand whether inventory is supporting production or trapping cash.

Practical Review Routine

1. Calculate days in inventory monthly.
2. Compare with previous months.
3. Break down by raw material, WIP, and finished goods.
4. Review slow-moving and dead stock.
5. Check finished goods pending dispatch.
6. Review supplier MOQ impact.
7. Compare inventory days with production and sales trends.
8. Set action owners.
9. Track improvement without causing stockouts.
10. Review in management meetings.

Founder’s Note

At AICAN, we believe inventory should move with purpose. Stock that supports production is useful. Stock that sits without reason quietly weakens cash flow.

With Optiwise, we help SMEs see inventory movement clearly so stock decisions become more balanced and less fear-driven.

Learn more at About AICAN.

FAQs

What is Days in Inventory?

Days in Inventory measures how many days inventory stays in the business on average before being sold or consumed.

What is the formula for Days in Inventory?

Days in Inventory = (Average Inventory / Cost of Goods Sold) x Number of Days.

Is lower Days in Inventory always better?

Not always. Very low inventory days can create stockout risk if supplier lead times or demand are uncertain.

How can manufacturers reduce Days in Inventory?

Improve demand planning, reduce slow-moving stock, set reorder levels, improve production flow, and dispatch finished goods faster.

How does Optiwise help?

AICAN Optiwise connects inventory, purchase, production, dispatch, and reporting to improve stock movement visibility.