Guide
Shopify inventory forecasting: how to predict what to reorder
A practical method any Shopify store can use: sales velocity, lead times, seasonality and safety stock, with worked examples.
1. Measure sales velocity
Velocity is units sold per day. Take the last 28 days of sales for a variant and divide by 28. Skip days the item was out of stock, because zero sales on those days doesn't mean zero demand.
2. Adjust for seasonality
If you have more than a year of data, compare the upcoming month last year to an average month last year. If last November sold 2× a normal month, double the forecast for November. Cap the adjustment (we use 0.5× to 2.5×) so one odd spike doesn't blow up your order.
3. Calculate days of stock left
4. Find your order-by date
If that number is 5, you have five days to place the order before you risk running out.
5. Decide how much to order
Round up to the supplier's case pack or minimum order.
Worked example
| Sales, last 28 days | 171 units → 6.1/day |
| On hand | 160 |
| Days left | 160 ÷ 6.1 = 26 days |
| Supplier lead time | 21 days |
| Order in | 26 − 21 = 5 days (no safety buffer) |
| Order qty (30 days cover) | 6.1 × 51 = 311 − 160 = 151 units |
Want to try your own numbers? Use the reorder point calculator.
FAQ
Does Shopify have inventory forecasting?
Not as a dedicated feature since Stocky was retired on August 31, 2026. Shopify's Sidekick assistant can suggest reorders, but there's no built-in per-SKU forecast tied to supplier lead times.
How much sales history do I need to forecast?
A few weeks gives a usable sales pace. For seasonality you need about 13 months, so you can compare the same period last year.
Is AI forecasting better than a simple average?
For most small and mid-size stores, a recent sales average adjusted for seasonality is accurate enough and easy to check. Complex models matter more at large scale with many demand drivers.
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