Shopify Inventory Forecasting: How to Build a Demand Planning Report

Why Shopify's Native Reports Fall Short for Forecasting

Shopify gives you solid historical sales data, but it stops there. There is no built-in report that says "based on your sales trend, you should reorder 200 units of SKU-XYZ in the next 3 weeks." The platform shows you what happened, not what's likely to happen next.

For merchants running lean inventory or managing seasonal demand, that gap is expensive. You either overstock and tie up cash, or you run out and lose sales.

Step 1: Pull Your Historical Sales Data

Any demand forecast starts with clean historical data. In Shopify, go to Analytics > Reports > Sales by Product. This gives you unit quantities sold per product over time.

A few things to watch out for:

Shopify's default reports only show 90 days of data. If your business has seasonal patterns (holiday spikes, summer lulls), 90 days is not enough history to build a reliable forecast.

Deleted or archived products disappear from reports entirely, creating gaps in your data. If you've relaunched products under new SKUs, your trend lines will be incomplete.

Refunds and exchanges are sometimes included in sales totals, which skews your demand signal.

Step 2: Calculate Average Sales Velocity

Sales velocity is the simplest forecasting metric: units sold per day (or week) on average. Once you have it, you can project forward.

Formula: Sales Velocity = Units Sold / Number of Days

Example: If you sold 120 units of a product in the last 30 days, your velocity is 4 units per day. If your lead time from supplier is 14 days and you want 7 days of safety stock, your reorder point is (4 x 14) + (4 x 7) = 84 units.

This is basic but surprisingly powerful. Most merchants who run out of stock are not tracking velocity at all.

Step 3: Account for Trends and Seasonality

Flat averages work if demand is stable. For seasonal businesses, you need to layer in trend data.

Look at year-over-year growth rates. If you sold 120 units in June 2024 and 150 in June 2023, your June 2025 forecast might start at 144 units (factoring in a 20% growth trend).

You can do this manually in a spreadsheet by exporting from Shopify. The challenge is getting enough historical data and doing it for every SKU, not just your top sellers.

Step 4: Build the Report (Your Options)

There are a few ways to build a working inventory forecasting report:

Shopify Reports + Google Sheets: Export your Sales by Product data, import into Sheets, and build a velocity calculator. This works but is manual and breaks every time you export a new file.

Dedicated Inventory Management Apps: Tools like Prediko or Inventory Planner are built specifically for this. They connect to Shopify, pull historical data, and generate reorder suggestions. Good choice if inventory planning is your core problem.

Product Analytics with Forecasting: If you want forecasting alongside product-level performance data (views, conversion rates, price analysis), a product analytics tool can give you demand forecasting as part of a broader picture.

A Better Approach: Sales Data with Built-In Forecasting

One limitation of Shopify's native reports is the 90-day data window. Building a reliable forecast requires at least 12 months of history, ideally 24.

Datma imports up to 2 years of historical sales data when you install it. Its forecasting report uses that full history to project end-of-month sales by product, so you can see not just what sold but what's likely to sell. It works at the variant level, which matters if a product has multiple sizes or colors with different demand patterns.

Combined with product-level views, conversion rates, and price change analysis, this makes it easier to understand not just "how much will I need" but "which variants are trending and which are fading."

What to Do Right Now

If you're starting from scratch, pick one of these actions this week:

1. Export your last 90 days of Sales by Product from Shopify Analytics and calculate velocity for your top 20 SKUs.

2. Identify which products you've restocked reactively in the past 6 months. Those are your highest-risk SKUs and should get a reorder buffer.

3. If you have seasonal products, pull year-over-year data now, before the season hits, not after.

Demand planning doesn't need to be sophisticated to be useful. Even a simple velocity calculation beats guessing, and it's something most Shopify stores can set up this week with existing data.