Inventory how-to

How to forecast when your store is growing fast

Use a short, recent sales window instead of a long average, and adjust it when you know something is changing on purpose, like a new ad campaign or a wholesale deal.

Short answer: Use a short, recent sales window instead of a long average, and adjust it when you know something is changing on purpose, like a new ad campaign or a wholesale deal. Fast growth makes old averages understate demand, so you have to lean on recent trend plus judgment, not just history.

Why growth breaks simple averages

If you average the last 6 or 12 months of sales, a fast-growing product looks slower than it actually is right now. The oldest weeks drag the average down and your reorder quantities end up too small, which causes stockouts right when demand is highest.

Shorten the window, watch it often

During fast growth, a shorter recent window, like the last 2 to 4 weeks, reacts faster than a long one. Check it weekly instead of monthly. If sales keep climbing week over week, expect your forecast to keep climbing too, and plan to reorder more often rather than trying to guess one big number far in advance.

Add a manual buffer on top of the numbers

No forecast method can know about a TikTok post going out tomorrow or a new wholesale account starting next month. When you know growth is about to jump, add a manual buffer to the suggested order quantity, and shorten your safety days temporarily so you reorder sooner rather than later. Pull the buffer back down once growth levels off.

Watch lead time risk more closely

Fast growth means you are drawing down stock faster, so any delay from a supplier hurts more. Confirm lead times with suppliers directly during a growth period instead of trusting the number on file, and consider raising safety days for your top sellers until growth stabilizes.

Step by step

  1. List your top 10 SKUs by recent sales and check growth trend weekly, not monthly.
  2. Shorten the sales window used for forecasting those SKUs to the last 2 to 4 weeks.
  3. Add a manual percentage buffer to suggested order quantities if you expect a specific demand spike.
  4. Temporarily cut safety days for fast-growers so reorder points trigger earlier.
  5. Confirm actual lead times with suppliers rather than relying on old estimates.
  6. Reorder in smaller, more frequent batches instead of one large order based on a guess.
  7. Review and reset the buffer and safety days once growth slows back to a steady rate.

Worked example

Say a SKU sold 4 units a day for months, then jumped to 10 units a day over the last two weeks. A 6-month average would still show something like 5 units a day, which is too low. Using the last 2 weeks instead, daily sales is 10. Lead time is 14 days and safety days is 5, so reorder point is 10 x (14 + 5) = 190 units. If on hand is 80 and nothing is on order, and you want 30 days of cover, order quantity is 10 x (14 + 30) - 80 = 360 units, rounded up to the supplier's case pack.

How SteadyShelf helps

SteadyShelf's default 28-day sales window already reacts faster than a long average, which helps during growth, and you can see the order-by date update as sales speed up. It does not know about upcoming marketing pushes or new wholesale deals, so during a known growth spurt you still need to manually bump the suggested order quantity or move the order-by date earlier yourself.

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

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FAQ

Will SteadyShelf automatically detect that my store is growing and adjust forecasts on its own?

It adjusts naturally because it uses a recent 28-day sales window, so rising sales feed into the forecast quickly. It does not predict future spikes from campaigns or new accounts, so you still need to add a manual buffer for anything you know is coming.

Should I increase safety days or decrease them during fast growth?

Decrease them for fast-growing SKUs so the reorder point triggers sooner, since you are burning through stock faster than before. At the same time, confirm lead times are still accurate, since a longer real lead time can offset the benefit of shorter safety days.

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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