Inventory how-to

How to adjust safety stock for peak season

Raise safety days per SKU before peak starts, based on how much your sales volatility increases and how firm your supplier lead times stay.

Short answer: Raise safety days per SKU before peak starts, based on how much your sales volatility increases and how firm your supplier lead times stay. Do it in two steps: increase safety days for the ramp-up period, then increase them again for the peak weeks themselves, and set a reminder to bring them back down after.

Why safety stock needs to change for peak

Safety stock exists to cover the gap between what you expect to sell and what you might actually sell, plus delays from your supplier. In peak season both sides get worse. Demand swings more day to day, and suppliers often slow down because they are busy with everyone else's peak orders too.

If you leave safety days at your normal setting, your reorder point stays too low right when you need more buffer. You will see stockouts hit your best sellers first, because they are the ones with the highest daily sales multiplying a too-small safety day number.

How to size the increase

Look at last year's peak period if you have it. Compare daily sales in peak weeks against your normal 28-day average. If a SKU sold at roughly double its normal rate during peak, that is a sign the safety buffer needs to grow, not just the base forecast.

Also check your supplier's lead time during peak. If they usually ship in 7 days but told you to expect 14 during peak, that extra week needs to be added to lead time, and safety days should cover the uncertainty around whether it will actually be 14 or longer. A rough rule: if peak demand is harder to predict, add safety days on top of the longer lead time rather than instead of it.

When to make the change and when to revert

Make the change two to three lead-time-cycles before peak starts, so the first peak-driven order already reflects the new numbers. Doing it at the start of peak is too late, since the order you place then will not land until peak is already underway.

Set a calendar reminder to drop safety days back down once peak ends. Carrying peak-level safety stock into the slow season ties up cash in excess inventory and increases the chance of markdowns later.

Step by step

  1. Pull last year's daily sales for peak weeks per SKU and compare to your normal 28-day average
  2. Ask each supplier what lead time to expect during peak, in writing
  3. Increase lead time in your reorder point calculation to match the supplier's peak quote
  4. Add extra safety days on top, sized to how much more volatile peak demand looked last year
  5. Apply the changes two to three lead-time-cycles before peak starts
  6. Place and track peak orders closely, since case pack minimums may force rounding up
  7. Set a reminder to revert safety days to normal levels once peak ends

Worked example

Say a SKU normally sells 4 units a day, with a 10-day lead time and 4 safety days, giving a reorder point of 4 x (10+4) = 56 units. Last year during peak this SKU sold 9 units a day, and the supplier's lead time stretched to 15 days. For peak you set daily sales to 9, lead time to 15, and raise safety days to 6 to cover the extra uncertainty. New reorder point: 9 x (15+6) = 189 units. Once peak ends, you drop the daily sales figure back to its normal average and safety days back to 4, cutting the reorder point back down to avoid overstocking.

How SteadyShelf helps

SteadyShelf lets you set safety days per SKU and per supplier, so you can raise them ahead of peak and the reorder dates and suggested quantities update automatically from your 28-day sales window. It does not automatically detect peak season or change safety days for you, and once you have about 13 months of history its seasonality adjustment helps but you still need to manually raise and then lower safety days around the actual peak dates.

$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

Should I increase safety stock for every SKU before peak, or only some?

Only increase it for SKUs where peak sales actually spike or where the supplier's lead time gets longer during peak. Applying blanket increases across your whole catalog ties up cash in slow-moving items that do not behave differently in peak, so check last year's numbers per SKU first.

What if I do not have last year's peak data because the product is new?

Use a similar existing product as a proxy, one with comparable price point and demand pattern, and apply a similar peak multiplier to its normal daily sales. Keep a close eye on actual sales once peak starts and adjust the safety days or reorder point manually if the new product behaves differently than expected.

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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