Inventory how-to

How to plan inventory for a store with steady demand

For steady demand, inventory planning comes down to three numbers per SKU: how fast it sells, how long it takes to get more, and how much safety buffer you want.

Short answer: For steady demand, inventory planning comes down to three numbers per SKU: how fast it sells, how long it takes to get more, and how much safety buffer you want. Set a reorder point from those numbers, check stock against it regularly, and order in case-pack quantities that cover a fixed number of days.

Why steady demand is the easy case

Steady demand means your daily sales rate does not swing much week to week. This is good news. You do not need complex seasonal models. A simple average of recent sales is a reliable predictor of near-term sales.

The core formula

Reorder point = daily sales x (lead time in days + safety days). When your stock on hand drops to this number, it is time to order. Order quantity = daily sales x (lead time + days of cover) minus (stock on hand + stock on order). Round the result up to the supplier's case pack or minimum order quantity.

Set sensible safety days

Safety days cover the gap between your forecast and reality, and any delay from your supplier. For steady sellers with a reliable supplier, 5 to 10 safety days is usually enough. If a supplier has missed lead times before, add more.

Review on a fixed schedule

Even with steady demand, check your reorder points weekly. Demand drifts over time, and a weekly check catches that drift before it causes a stockout. Update your daily sales average using a recent window, such as the last 28 days, rather than all-time history, so the number reflects current reality.

Step by step

  1. List each SKU with its current on-hand stock and supplier lead time.
  2. Calculate a daily sales rate from the last 28 days of orders for each SKU.
  3. Set a safety day buffer per supplier based on how reliable their lead times are.
  4. Calculate the reorder point for each SKU: daily sales x (lead time + safety days).
  5. Decide a days-of-cover target for orders, such as 45 or 60 days.
  6. Round order quantities up to the supplier's case pack or minimum order size.
  7. Recheck stock against reorder points weekly and place orders as SKUs hit the threshold.

Worked example

A store sells a candle at 6 units a day on average over the last 28 days. The supplier's lead time is 10 days and the store adds 5 safety days, so the reorder point is 6 x (10 + 5) = 90 units. Stock on hand is currently 100, so no order yet. The store wants 60 days of cover and has nothing on order, so when it does order, the quantity will be 6 x (10 + 60) - 100 = 320 units, rounded up to the nearest case pack of 24, which is 336 units.

How SteadyShelf helps

SteadyShelf automates exactly this: it tracks the 28-day sales rate per variant, calculates the reorder point from each supplier's lead time and safety days, and gives you an order-by date with a suggested quantity rounded to case packs. It will not forecast separately per store location or handle bundles, so if you stock the same SKU across multiple warehouses you will need to split those numbers 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

Do I need 13 months of sales history before I can plan inventory for steady demand?

No. For steady, non-seasonal demand, a shorter recent window like 28 days of sales is enough to set a reliable daily sales rate. Longer history matters more once you want to account for seasonal swings.

What if my supplier has a minimum order quantity bigger than what the formula suggests?

Order the minimum and treat the extra stock as additional days of cover. Recalculate your next order-by date based on the larger quantity, since it will last longer than your original days-of-cover target.

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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