The reorder point formula and safety stock

Posted by Thomas Wong

How little is too little? That’s exactly what your Reorder Point will help you determine. Let’s talk about the concept of reorder points, safety stock, and how to put those numbers together to make sure you have the right amount of stock on-hand.

When you start your business off you’re probably making orders based on your gut instinct and the money you have on hand, but your reordering can be even more efficient with a reorder point formula. This post will show you what that is, and what numbers you’ll use to come up with a reorder point.

How can I calculate my reorder point?

The thing to know about a reorder point is that it’s not a static number. It’s based on your own purchase and sales cycles, and it varies on a per-product basis. However, once you have a handle on patterns in your purchase and sales orders for a particular product, you’re ready to start putting the variables together.

The reorder point formula is:

reorder point formula equals open parentheses average daily unit sales times delivery lead time close parentheses plus safety stock

Calculating average daily unit sales

Take the case of Archon Optical and their Ghost glasses. Here are the sales of the Ghost over the last three months:

Table of Average Daily unit sales for ghost glasses. January Sales: 65, February Sales: 72, March Sales: 53

If we total those numbers, we get 190 total units sold over the past 90 days. That means that the daily sales for the Ghost is 2.11 per day.

Calculating average delivery lead time

Average delivery lead time is simply the amount of time it usually takes for your shipments of a particular product to arrive. You’ll want to have a couple of purchase orders on-hand to check the numbers for this, as the delivery times can vary based on the quantity you order, as well as when you order it. There are a few different ways to calculate this, but averaging things out over the past few months can help provide some context.

In the case of Archon Optical, here are a few purchase orders for the last three month of Ghost shipments:

15 days total delivery time / 3 orders total = 5 days lead time on average

If you add the total delivery time (15 days ) and divide it by the number of orders (3 orders), then that’s an average lead time of five days for the product to arrive.

Calculating safety stock based on extra days of demand

The idea of safety stock is similar to the idea of a reorder point, which is the stock quantity at which you will generate a new purchase order for that product. A reorder point can be the same as your safety stock number, but it’s usually higher to factor in the lead time.

Some numbers you’ll want to take into account as you decide on a safety stock level are: average daily sales and the daily average that product used in work orders (if applicable), as well as the lead time. but for this article, we’ll keep things simple by calculating safety stock based on two weeks of extra demand.

Since the average daily sales for the Ghost are 2.11 (as calculated earlier on this page), that means the safety stock for Ghost is about 14 x 2.11 = 29.54, or 30 if you round the number up. After all, nobody really orders 0.54 pairs of glasses.

[We’ve also written a more detailed article on safety stock, if you’d like to calculate it based on lead-time demand.]

Putting the numbers together

Now that we’ve got all of the Archon Optical numbers down, we’re ready to put together a reorder point for the Ghost.

(2.11 x 5) + 30 = reorder point of 40.5

This means that, once the quantity on-hand for the Ghost glasses hits roughly 40 or 41, the people at Archon Optical know to put in another purchase order for more of the product. Because they’ve built an average delivery lead time into the reorder point, the extra Ghost glasses should arrive before Archon ever dips below the amount of safety stock.

However, even if there are production shortages or delays in shipment, Archon Optical’s safety stock ensures that they can continue to sell the Ghost for two weeks before they run out of stock.

Setting up automatic reminders for reorder points

Reorder points are incredibly powerful for keeping your business running smoothly. It’s one thing to understand the concept, but they’re no use to you if you aren’t set up to reorder in a timely manner.

If you’re a spreadsheet user, you can use conditional formatting for the quantity value of specific cells. It’s a bit of work up front because you’ll have to set it up for each individual cell, but you can set Excel or Google Sheets so that cells turn red the moment they dip below your reorder point, which will warn you when you need to start on a new purchase order.

Handle your reorder points with inFlow!

You can make reordering even easier and more efficient with inFlow Cloud. You can attach a reorder point to every single product in your business, and these products will automatically show up on a Reorder Stock screen when you’re running low.

You can start your free inFlow Cloud trial today!

Thomas Wong

About Thomas Wong

Thomas is a 100% human being who splits his time between supporting inFlow's customers with his mind, writing medium-sized articles with his keyboard, and taking large photographs with his camera.

Have a question or comment? Let us know below!

    1. Good question, Amalina. We’ll be writing a more specific article on safety stock in the future, but the quick answer is: it’s the amount of extra stock that you keep on hand to ensure that your business is unaffected by shortages in supply (for example, if your purchase order is delayed by two weeks). It’s like a rainy day fund, but for inventory.

      [Update: our safety stock article is now published at https://www.inflowinventory.com/blog/how-to-calculate-your-safety-stock/ ]

  1. Hi, please can you tell the difference between minimum stock level and the safety inventory? If there is and difference whats the essence of knowing the minimum level then? Thank you

    1. Hi Michael, the reorder point basically becomes your minimum stock level, because you’ll want to reorder once you fall *below* the reorder point. So if you had a reorder point of 20 and you reached 18 or 19 pcs on hand, you’d want to reorder. You’d be below your minimum stock level.

      Safety stock is calculated as part of that reorder point, the more safety stock you decide on, the higher your reorder point will be.

    1. Hi Tom, thanks for pointing this out! Sorry about that — we’ve made the correction in the post.
      – Thomas

  2. Question.
    The following is the consumption of rice in certain hotel.
    maximum consumption=6000kg per week.
    minimum consumption=4000kg per week.
    Reoder period 4-6 weeks
    Reorder quantity 30,000kg
    Calculate
    i)Re-order period.
    ii) Minimum stock level.
    iii)Maximum stock level
    iv)Average stock level
    How can i calculate this?