Inventory glossary
What is Seasonality?
Seasonality is the predictable rise and fall in sales that repeats around the same time each year, tied to holidays, weather, or shopping events.
Seasonality matters because it breaks simple forecasting methods that just average recent weeks. If you plan reorders based on October sales alone, you will under-order for November and get caught short during your busiest month, or over-order for January and sit on dead stock.
To use it well, look at what happened in the same period last year, not just last month. Adjust your order quantities and order-by dates ahead of known peaks like holidays or back-to-school, and build in extra lead time since suppliers get busier too during those windows.
Example
A candle store sells 40 units a week most of the year but sold 160 units in the week before last Christmas. If the owner only looks at the prior four weeks of average sales to set this December's order, they might plan for 40 a week and run out fast. Using last December's actual numbers, they plan for 150 to 160 units that week instead.
Common mistakes
- Using a recent-weeks average to forecast a holiday spike, which badly understates demand.
- Ignoring that suppliers also face seasonal delays, so lead times can stretch right when you need stock fastest.
- Treating a one-off spike (a viral post, a sale event) as seasonality when it was not tied to the calendar.
Seasonality and SteadyShelf
SteadyShelf's forecasts factor in sales history by SKU so seasonal swings from past years feed into order-by dates and suggested quantities, instead of relying on a flat recent average.
Work it out for your own products with our free tool: Shopify inventory forecasting.
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Related terms
Demand forecasting · Demand variability · Lead time demand · Safety stock · Weeks of supply
FAQ
How is seasonality different from normal demand variability?
Demand variability is the everyday ups and downs in sales that happen without a clear pattern. Seasonality is a repeating pattern tied to a specific time of year, like holidays or weather, that you can plan around using past data from the same period.
How far ahead should a small store plan for a seasonal peak?
Start by working back from the peak date using your supplier's lead time, then add extra time since suppliers are often slower during their own busy season. A store expecting a December rush might need to place orders by October if lead time plus supplier delays add up to eight or nine weeks.
Let SteadyShelf do this math for every SKU
Order-by dates per supplier, seasonal forecasts and draft POs for your Shopify store. $29/month after a 30-day free trial.
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