Forecasting at product level hides the real problem. "We sold 200 hoodies last month" sounds fine until you notice 80 of them were Medium Black and you are now out of Medium Black, while 30 XXL Yellow sit on the shelf. Stock runs out one variant at a time, so that is the level to plan at.
You do not need special software to start. A spreadsheet, your Shopify sales report and one simple formula will get a small store most of the way. Here is the method we suggest, with a worked example.
Sales velocity per variant
Velocity is how many units of a variant you sell in a set period, usually per day or per week. In Shopify, go to Analytics, then Reports, and open a sales report broken down by product variant. Export the last 8 to 12 weeks and divide units sold by the number of days to get an average daily rate.
Use recent weeks, not the whole year, unless the product is very steady. And remove days when the variant was out of stock, or your rate will look lower than real demand. If the variant breakdown is missing or looks wrong, our guide to missing variant data in Shopify Analytics explains the common causes.
Reorder point
The reorder point is the stock level that tells you to order more. The basic formula is:
Reorder point = (Lead time in days × Daily velocity) + Safety stock
Lead time is the number of days from placing an order with your supplier to having the stock ready to ship. Safety stock is a buffer for slow deliveries or a busy week. Many merchants start with a week or two of average sales as their buffer and adjust it after a few cycles.
Worked example
| Variant | Daily velocity | Reorder point (21-day lead time + 7 days safety) |
|---|---|---|
| Hoodie, Medium, Black | 2.5 | (21 × 2.5) + (7 × 2.5) = 70 |
| Hoodie, Large, Black | 1.8 | (21 × 1.8) + (7 × 1.8) = 50 |
| Hoodie, XXL, Yellow | 0.2 | (21 × 0.2) + (7 × 0.2) = 6 |
When Medium Black drops to 70 units, place an order. XXL Yellow can sit at single digits without risk. The same product needs very different treatment per variant, which is the whole point.
To get a nudge when a variant crosses its reorder point, set up an alert. Our guide to low-stock alerts for variants shows how to do it with Shopify Flow so the email goes out without you checking every day.
Seasonality
If you have a year of history, compare this week's velocity with the same weeks last year. Gift products pick up sharply before the winter holidays, and back-to-school or Mother's Day bring their own peaks. Raise your velocity estimate and order earlier, typically 30 to 60 days before the peak, because supplier lead times often stretch at the same time your sales climb.
For a new product with no history, use a similar product's numbers as a starting point and review weekly for the first couple of months.
Apps
A spreadsheet is enough for a small catalog. Once you have hundreds of active variants, several suppliers or more than one warehouse, a forecasting app saves real time. Inventory Planner and Cin7 are two common choices that calculate reorder points per variant and can draft purchase orders. Shopify has also offered its own Stocky app for POS Pro merchants; check its current availability, as Shopify has been changing its inventory tools.
Multi-location stores
If you stock at more than one location, calculate velocity per location. A variant that sells well online may barely move in a retail shop. Our guide to multi-location inventory for variants covers how Shopify tracks stock across locations.
Personalized and print-on-demand products
Print-on-demand products do not need forecasting at all, because the partner prints each item after the order arrives. Personalized products that you make in-house are different: you still stock the blanks. A store selling engraved tumblers forecasts the plain tumblers by color and size, while the engraving text is saved on each order as a line-item property and never affects stock. That keeps your variant list small and your forecast simple. If you are still deciding between holding stock and printing on demand, see our comparison of POD vs buying inventory.
Frequently asked questions
How to forecast Shopify variant inventory?
Work out each variant's average daily sales from recent weeks, then set a reorder point equal to daily sales times your lead time in days, plus some safety stock. Reorder when stock reaches that number.
Best forecasting app for Shopify?
Inventory Planner and Cin7 are common choices for variant-level forecasting and purchase orders. Shopify's Stocky app has served POS Pro merchants, but check its current status before relying on it.
How to handle seasonality in forecast?
Compare weekly sales with the same weeks last year and raise your estimate for peak periods. Order 30 to 60 days ahead of the peak, since supplier lead times often get longer at the same time.
Manual vs automated forecast?
A spreadsheet works well for a small catalog with one supplier. Once you manage hundreds of active variants, several suppliers or multiple warehouses, an app that recalculates reorder points automatically saves a lot of time.
Does POD need forecasting?
No. Print-on-demand partners produce each item after it is ordered, so there is no stock to forecast. It only applies to products you hold in stock, including blanks you personalize yourself.
Multi-location forecast?
Yes. Calculate velocity separately for each location and send reorders to the location that actually sells the variant.
Low-stock alert setup?
Use Shopify Flow to watch variant inventory and send an email or task when it drops below your reorder point. Set the threshold per variant if sales differ a lot.
Inventory turnover metric?
Turnover is cost of goods sold divided by average inventory value for the period. There is no single right number, so compare it with your own past results and look for variants that turn much slower than the rest.
Related reading
Sources & further reading
Primary sources referenced in this article. We link to official platform documentation and standards bodies rather than secondary summaries so you can verify claims directly.
- Shopify Help Center: Product variants
- Shopify.dev: Product variant limits
- Shopify Help Center: Line item properties (customization)
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