How to Forecast Inventory on Shopify (Without Stocky)
Learn how to forecast inventory on Shopify using sales velocity, reorder points, and days of stock. Step-by-step guide with formulas and examples.
Stocky used to handle inventory forecasting for Shopify POS Pro users. Now that it's being discontinued, many merchants are left wondering: how do I predict what to order and when?
The good news: inventory forecasting isn't rocket science. Here's how to do it — with or without an app.
The 3 Numbers You Need
Every inventory forecast boils down to three numbers:
1. Sales Velocity
How many units of each product you sell per day.
Sales Velocity = Units Sold ÷ Number of Days
Example: You sold 90 units of "Blue T-Shirt XL" in 30 days
→ Velocity = 90 ÷ 30 = 3 units/day
2. Days of Stock Remaining
How many days your current inventory will last at the current sales rate.
Days of Stock = Current Stock ÷ Daily Velocity
Example: You have 45 units in stock, selling 3/day
→ Days of Stock = 45 ÷ 3 = 15 days
3. Reorder Point
The stock level at which you should place a new order.
Reorder Point = (Lead Time + Safety Stock) × Daily Velocity
Example: Supplier takes 7 days, you want 3 days buffer, velocity is 3/day
→ Reorder Point = (7 + 3) × 3 = 30 units
→ When stock hits 30, order more
Method 1: The Spreadsheet Approach (Free)
If you have fewer than 50 SKUs, a spreadsheet works fine.
Step 1: Export Your Orders
In Shopify Admin → Analytics → Reports → "Sales by product variant"
- Set date range to last 30 days
- Export as CSV
Step 2: Calculate Velocity
In Google Sheets:
Column A: Product Name
Column B: Units Sold (30 days)
Column C: Current Stock (from Products export)
Column D: =B2/30 (daily velocity)
Column E: =IF(D2>0, C2/D2, "No sales") (days of stock)
Column F: =(7+3)*D2 (reorder point, 7-day lead time + 3-day buffer)
Column G: =IF(C2<F2, "⚠️ ORDER NOW", "OK")
Step 3: Review Weekly
Set a calendar reminder every Monday: open the sheet, update stock numbers, check Column G.
Pros: Free, you understand the math. Cons: Manual, error-prone, doesn't scale past ~50 SKUs.
Method 2: Use an App (Recommended)
If you have 50+ SKUs or multiple locations, automate this with an app.
Apps like Restocky do all of the above automatically:
- Pull your sales data from Shopify in real-time
- Calculate velocity per SKU continuously
- Alert you via email or Slack when items hit the reorder point
- Generate purchase orders with recommended quantities
The math is the same — the app just runs it for you, every day, across all SKUs.
Common Forecasting Mistakes
❌ Using too short a window
Don't calculate velocity from just 7 days of data. A single viral TikTok could skew everything. Use 30 days minimum, 90 days for stable products.
❌ Ignoring lead time
Your reorder point must account for how long your supplier takes to deliver. If they take 14 days and you order when stock hits zero, you'll be out of stock for 2 weeks.
❌ Not adding safety stock
Supply chains aren't perfect. Always add a buffer (typically 3–7 days of extra stock) to your reorder point.
❌ Treating all products the same
Your best-seller with 10 orders/day needs different treatment than a slow-mover with 1 order/week. Set different lead times and safety stock per product category.
❌ Forgetting about seasonality
A 30-day average in January won't predict February (Valentine's Day) or November (Black Friday). For seasonal products, look at the same period last year if possible.
The 80/20 of Inventory Forecasting
You don't need a PhD in supply chain management. For most Shopify stores:
- Calculate velocity (units/day per SKU)
- Know your lead times (days until supplier delivers)
- Set reorder points (lead time + buffer × velocity)
- Check weekly (or set up automated alerts)
This alone prevents 80% of stockouts. Everything else — seasonal modeling, trend analysis, AI prediction — is optimization on top of a solid foundation.
Next Steps
- Under 50 SKUs? Download our free velocity spreadsheet template and start today
- Over 50 SKUs? Try Restocky free — automates everything above
- Coming from Stocky? Read our complete migration guide
