Inventory Days Calculator - By Verve AI (Free Google Sheet Tool)
Understanding how quickly your inventory sells is one of the most important metrics in retail and e-commerce. High inventory days means cash is tied up, overstock accumulates, and purchasing becomes guesswork. Low inventory days means faster turns, healthier margins, and better cash flow. To make this easier, we’ve created a free Inventory Days Calculator in Google Sheets — simple, accurate, and built for operators who want clarity without spreadsheets becoming a full-time job.
This page includes the embedded tool, a downloadable version, benchmark data, and a complete walkthrough of the DIO (Days Inventory Outstanding) formula.
How to Use the Inventory Days Calculator
The calculator is designed to be fast and frictionless. You only need four inputs:
1. **Opening inventory** for the period
2. **Closing inventory** for the same period
3. **COGS (Cost of Goods Sold)**
4. **Period length** (defaults to 365 days)
Once you enter your numbers, the sheet automatically calculates:
Average inventory
Inventory turnover
Inventory days (DIO)
A traffic-light signal showing whether your inventory performance is *good*, *OK*, or *high-risk*
This tool works for Shopify merchants, D2C brands, wholesalers, or anyone managing physical goods. You can embed it into your weekly reporting, share it with your team, or use it to benchmark your stock health.
Get Your Free Inventory DaysCalculator
You can make a full coopy from the link below:
Inventory Days Formula (With Example)
The Inventory Days formula follows standard accounting and supply-chain methodology:
1. Average Inventory
(Opening Inventory + Closing Inventory) / 2
2. Inventory Turnover
COGS / Average Inventory
3. Inventory Days (DIO)
(Average Inventory / COGS) × Period Length (e.g., 365)
Worked Example
Let’s say over one year you recorded:
Opening inventory: £10,000
Closing inventory: £14,000
COGS: £60,000
Period length: 365 days
Step 1 — Average Inventory
(10,000 + 14,000) / 2 = 12,000
Step 2 — Inventory Turnover
60,000 / 12,000 = 5.0
Step 3 — Inventory Days
(12,000 / 60,000) × 365 = 73 days
Inventory Days Calculator - How to Interpret
73 days means stock is sitting for around 2.5 months before being sold — a potential warning sign that you’re holding too much cash in inventory.
Inventory Days Benchmarks by Industry
Inventory Days varies significantly by industry. Here are common benchmark ranges:
Grocery & Convenience: 7–21 days
D2C Food & Beverage: 14–35 days
Beauty & Cosmetics: 20–45 days
General E-commerce (mixed SKUs): 30–60 days
Fashion (Fast Fashion): 30–60 days
Premium Fashion: 60–120 days
Electronics: 45–90 days
Furniture & Homeware: 60–150 days
Pet Products: 25–50 days
If your Inventory Days figure is higher than your industry benchmark, it typically means you are:
Over-ordering
Holding too much depth in slow movers
Missing key demand signals
Tying up cash that could be deployed elsewhere
Lowering Inventory Days improves working capital, reduces write-offs, and boosts profitability.
Download the Inventory Days Calculator (Google Sheets)
If you prefer your own copy of the calculator, you can download the Google Sheets version below:
This version includes:
Fully unlocked formulas
An example walkthrough
Benchmarks tab
Notes on methodology
A Verve AI CTA panel for deeper forecasting tools
Feel free to duplicate it, customise it, or share with your team.
Automate Inventory Days Tracking with Verve AI
If you run a Shopify store, you’ve probably noticed the biggest challenge isn’t calculating Inventory Days once — it’s tracking them reliably over time.
That’s where Verve AI comes in.
Verve AI automatically:
Forecasts demand at variant level
Calculates reorder points using supplier lead times
Highlights SKUs with high Inventory Days
Recommends optimal purchase quantities
Helps prevent both stockouts and overstock
Generates purchase orders in a few clicks
Instead of maintaining spreadsheets or manually analysing inventory health, Verve AI brings everything directly into your Shopify admin.
👉 View Verve AI on the Shopify App Store
If you like this calculator, Verve AI gives you the fully automated version — with real sales data, real inventory, and real forecasting intelligence powering it behind the scenes.