# Safety Stock Formula: Easily Calculate Optimal Stock Levels

However, during peak periods, you sell up to 15 products per day, and delays in inventory shipment mean it takes up to 18 days for products to arrive at your warehouse. Despite inventory management myths that state the contrary, safety stock is essential for your business. That’s because even the best data analysts in the world can’t accurately predict customer desires or unexpected mishaps along the supply chain. The amount of buffer inventory you have will largely depend on the type of products you sell, your average production or order lead times, as well as your historical inventory data. Luckily, safety stock formulas help you determine the right amount of inventory to keep orders flowing without incurring extra holding costs. There are several different ways to calculate safety stock levels for your products.

• You should always safeguard your inventory by looking at the standard deviation time.
• This can, and does lead to significant stock outages down the line, variances in inventory control across the business and ultimately a confused and ineffective inventory management system.
• In this method, companies set a fixed level of safety stock for their goods.

These data are, among others, are obtained with the “STDEV” formula on Excel. In this example, you should focus your efforts primarily on items of category A. Activity-based costing, also known as the ABC method is based on the same principles as the Pareto rule, but with a more precise breakdown. Also known as the 80/20 rule, the Pareto principle can be applied in many fields (sales management, marketing, project management, etc.). You can use a standard deviation calculator to help in your computations.

## Replenish stock at the right time

In other words, companies maintain anticipation inventory when they expect a change in demand in the near future. This kind of stock benefits retailers by ensuring they can meet customer demand (even as that demand is surging). The truth is, no formula is perfect, and the real world is much more variable than what standard deviation can capture. That’s why you should never rely on the exact number output by the safety stock formula.

Let’s say you expected a shipment in 14 days, but it actually took 15, 12, 17, 14, and 19 days to arrive (a variance of 1, -2, 3, 0, and 5). ​Many factors affect demand, seasonality, holiday sales, weather, economics, and political climates can all play a role, so this is not an exact science. To safeguard against the hazards at either end of the spectrum, manufacturers apply a formula to calculate the correct levels of inventory to keep on their shelves. Lost How To Calculate Safety Stock? Safety Stock Formula And Calculation customers, complaints, increased transport cost and more can result in businesses witnessing massively reduced profits, reputation and even failing. The software can flag discrepancies and problems before they arise and inventory management can move from a reactionary process to a proactive and seamless operation. While we have covered reorder points in detail in other articles it is worth revisiting the reorder point formula here when used with safety stock.

## Normal Distribution

Entrepreneurs and Operation Managers who understand their product and have data on past sales can expect higher inventory efficiency and higher revenue returns. In a perfect world, this will mean that you won’t ever need to use your safety stock but it’s highly unlikely this will happen. Safety stock is there to cover you in times of variability in demand and lead time. Safety stock will stop issues with your lead time and limit the impact of your service rate.

• Safety stock helps you hold the right amount of buffer stock in case of unforeseen circumstances, so make sure you don’t default it to zero.
• He is a fictional character for better illustrative purposes and also a mushrooming retailer.
• That said, incorporating the safety stock formula can give you a leg up on your competition when demand spikes and provide a much-needed insurance policy against stockouts.
• As a result, demand for the mug skyrockets and the business receives hundreds of orders over the next several days.

Safety stock management is a critical part of being a retailer and a manufacturer. It will help to reduce the chance of stock outs, which lead to inefficiency, unhappy customers, and ultimately, lost sales and reduced profits. Before you choose the right formula for your safety stock you must first consider the quality and quantity of your data. As data is a critical element in all of these calculations, a solid and reliable data set to work from is critical. If not, your calculations could be inaccurate causing more issues than it solves. Now that we have an idea of the six methods you can use to calculate safety stock, it’s important to know the limitations.

## Calculating safety stock with economic order quantity (EOQ)

Every time you hit a cap on how much stock you have available, that represents the additional sales you weren’t able to make. Next you’ll multiply the maximum daily usage https://kelleysbookkeeping.com/ by the maximum lead time. If your average is 100 units daily, but you’ve sold up to 150 units in a day, you would use 150 as your maximum daily usage in the calculation.

The reorder point calculation can be done with, or without safety stock levels incorporated. Service factor, also referred to as the Z-score or Z-value in safety stock formulas, is your desired service level, transposed into a statistical score for easier calculation. To calculate safety stock with it, you need to know your
maximum lead times as well as your maximum demand. For brands with the data needed to calculate those specific variables, the more complex formulas (like Greasley’s method) will likely pinpoint safety stock levels with greater accuracy and assurance.

Not to worry — this step-by-step guide will show you everything you need to know about safety stock and how to calculate it for your business’s unique inventory levels. “D avg” represents the average amount of demand within a given period. For safety stock purposes, it’s most common to find the average daily demand. To do this, add the number of sales made in the given period and then divide that figure by the number of days in that period. Safety stock is about more than just having a few extra units available.

• If a business takes on orders based on miscalculated inventory levels, it can end up with orders it cannot fulfil.
• We then need to factor-in our desired service level to calculate safety stock.
• With ZhenHub, we provide the tools that allow greater control and visibility over your eCommerce logistics.