Inventory how-to

How to plan inventory for a store with lumpy demand

Lumpy demand means long stretches of low or no sales broken by sudden spikes.

Short answer: Lumpy demand means long stretches of low or no sales broken by sudden spikes. Smooth daily averages mislead you here, so plan with wider safety buffers, shorter review cycles, and manual judgment on top of the numbers. Treat forecasts as a starting point, not a final answer, for these SKUs.

Why averages fail you

A 28-day average sale rate hides the pattern of lumpy demand. If a SKU sold 0 units for 20 days then 40 units in 3 days, the average looks moderate but the real behavior is feast or famine. Ordering to the average often means you are out of stock during the spike and overstocked during the quiet weeks.

Widen your safety stock

For lumpy SKUs, add extra safety days on top of what you use for steady sellers. The goal is to cover the size of a typical spike, not just the average daily rate. Look at your past spikes and ask how many units sold in the worst 3 to 5 day burst, then make sure your reorder point can absorb that.

Shorten your review cycle

Check these SKUs more often than once a month. A weekly look lets you catch the start of a spike early and get a purchase order moving before you run out. Waiting for a monthly review often means you spot the spike only after it has already cost you sales.

Separate lumpy SKUs from your core catalog

Flag which products are genuinely lumpy, for example seasonal accessories, viral one-offs, or items tied to promotions. Do not let their pattern distort your view of steady sellers, and do not apply the same cover-days logic to both groups. Review the lumpy list on its own cadence and with more manual eyes on it.

Step by step

  1. List every SKU with irregular sales history over the last 6 to 12 months
  2. For each one, find the biggest burst: units sold in the worst 3 to 5 day stretch
  3. Set safety days high enough to cover that burst size, not just average daily sales
  4. Shorten your reorder check for these SKUs to weekly instead of monthly
  5. Keep a separate watchlist for lumpy SKUs so they do not skew decisions on your steady sellers
  6. When a spike starts, place the order immediately rather than waiting for the next scheduled review
  7. After each spike, update your notes on burst size so next season's buffer is more accurate

Worked example

Say a candle scent sold 2 units a day most days but jumped to 15 units a day for 4 days during a influencer mention last spring. Average daily sales over 28 days might compute to 4 units a day, but ordering reorder point = 4 x (10 day lead time + 5 safety days) = 60 units would not have covered the burst. Instead, using the burst rate: reorder point = 15 x (10 + 5) = 225 units gives enough buffer to survive a repeat spike without stripping the shelf bare.

How SteadyShelf helps

SteadyShelf's default forecast uses a 28-day sales window, which smooths out lumpy patterns the same way any average does. It will still give you an order-by date and suggested quantity, but for genuinely lumpy SKUs you should manually raise the safety days in the supplier settings and watch the weekly reorder email closely rather than trusting the suggested quantity as-is.

$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.

Related guides

All inventory how-to guides ยท Inventory glossary

FAQ

Can SteadyShelf detect which SKUs are lumpy automatically?

No. SteadyShelf does not label demand patterns for you. You need to identify lumpy SKUs yourself from sales history and then adjust safety days for those items manually.

Once SteadyShelf has 13 months of history, does it handle lumpy demand better?

At that point it can factor in seasonality, which helps with demand that repeats on a yearly cycle, like holiday spikes. It does not help with one-off or unpredictable bursts that have no seasonal pattern, those still need manual safety day adjustments.

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.

Get early access