Inventory how-to

How to forecast without Stocky

You can forecast demand manually using recent sales history and a simple formula, or use an app that automates it.

Short answer: You can forecast demand manually using recent sales history and a simple formula, or use an app that automates it. The core idea: find average daily sales per variant, then project that forward to decide reorder points and quantities.

Pick a sales window

Use a recent, representative period, usually the last 28 to 60 days. Shorter windows react faster to recent trends but are noisier. Longer windows smooth out noise but react slowly to changes. Pull sales per variant for the window from your store admin reports or export.

Calculate daily sales and reorder point

Divide total units sold in the window by the number of days to get average daily sales. Multiply that by the supplier's lead time plus a safety buffer (in days) to get your reorder point. When stock on hand drops to that number, it is time to order.

Turn forecasts into order quantities

Order quantity equals daily sales times the sum of lead time and days of cover you want to hold, minus what you currently have on hand and on order. Round up to the supplier's case pack size or minimum order quantity. Repeat this per variant, not just per product, since variants sell at different rates.

Account for seasonality and trends manually

If you have at least a year of history, compare the same period last year to spot seasonal swings and adjust the daily sales figure up or down by judgment. Without that history, watch for trend changes week over week and recalculate often rather than relying on a single static number.

Step by step

  1. Export unit sales per variant for the last 28 to 60 days.
  2. Calculate average daily sales per variant (units sold divided by days).
  3. Get lead time and set a safety day buffer per supplier.
  4. Calculate reorder point: daily sales x (lead time + safety days).
  5. Calculate order quantity: daily sales x (lead time + days of cover) minus (on hand + on order).
  6. Round quantities up to case pack size or supplier minimum.
  7. Recalculate weekly or whenever sales patterns shift.

Worked example

Suppose a variant sold 56 units over the last 28 days, so daily sales is 2 units. Lead time is 10 days and you want 5 safety days, so the reorder point is 2 x 15 = 30 units. You want 20 days of cover beyond lead time, so order quantity is 2 x (10 + 20) minus (18 on hand + 0 on order) = 60 - 18 = 42 units. If the supplier's case pack is 25, you round up to 50 units.

How SteadyShelf helps

SteadyShelf automates exactly this calculation per variant, using a 28-day sales window by default and adding seasonality once it has about 13 months of history, then gives you an order-by date and a suggested quantity rounded to case packs. It does not do per-location forecasts or multi-location transfers, so if you stock multiple warehouses you will still need to split or adjust quantities manually.

$29/month flat, unlimited products and suppliers, 30-day free trial. Run the numbers now with the free reorder point calculator.

SteadyShelf is launching on the Shopify App Store. Join early access to get the install link first.

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FAQ

What sales window should I use if my store has high day-to-day variance?

Lean toward the longer end, 45 to 60 days, so single spikes or slow days do not skew your average. If you have enough history, also compare against the same period last year to sanity check the number.

Do I need to forecast every variant separately or can I group by product?

Forecast per variant. Size and color variants often sell at very different rates, and ordering based on the product total will overstock slow variants and understock fast ones.

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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