Deciding Which Products to Stock in a Business

EricW

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Jul 28, 2011
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I run a small mail order business; Inventory is purchased from various vendors, stored in a warehouse, until it’s sold and shipped to the buyer. I have limited cash and limited storage space, so I would like to maximize profit by carrying the best possible mix of products.

On many of my sales, I do not charge the customer any shipping costs, as I pay for the shipping out of the profit in the item. The shipping costs for my items vary greatly since some items are light and others are heavy. So for a simplified example, if an item sells for $50.00, costs me $20.00 to ship, and $20.00 for the cost of the item, I have made $10.00 gross profit, or 20% gross margin. I always use gross margins to compare products; so if product #1 has a 20% margin, it must be better than product #2 that has a 15% margin. Lately I have been realizing that this may not be the best answer. Comparing these examples:

a. Product “a” sells for $200.00 including shipping. Item costs me $65.00, shipping costs me $95.00, leaving $40.00 in profit, 20% margin
b. Product “b” sells for $200.00 including shipping. Item costs me $145.00, shipping costs me $15.00, leaving $40.00 in profit, 20% margin

Although both of these examples have the same margin and profit, “a” is drastically better since I only have to lay out $65.00/pc inventory. When the customer pays me $200.00 and I prepare the shipping label, only then do I incur the shipping expense, for which I’ve already been reimbursed. So if I only compare products based on margin I’m not accounting for the fact that some products are very heavy, so the high shipping costs penalize them unfairly. Taking it to an extreme, if I had a product that cost me $50.00 to buy, $500.00 to ship, and sold for $600.00, the margin would look very low (under 10%), but I would be doubling my initial investment. This has me thinking maybe I should consider “markup”, instead of “margin”.

In addition I have to consider the absolute profit. Calculating my overhead and dividing it by the average number of items I sell gives me an expense of about $2.00 for every order. So buying an item for $0.25 that makes me $1.00 in gross profit would look great on a markup calculation, but would put me out of business.

I also have a space constraint, and products take various amounts of space to store. One item may take up 6 cubic feet, and other item only 1 cubic foot. If these items cost the same and sold for the same markup, I would much rather stock only the 1 cubic foot items, as I would have 6x the capacity in my warehouse. Further complicating matters is the fact that most of the vendors I deal with have minimum order requirements, say 100 pieces, so sometimes merchandise may sit on the shelf longer than desired, making the space used very valuable. It costs me about $0.35 per cubic foot of usable rack space per month. Of course the lower my asking price, the faster the merchandise will sell, and the less rack space required.

So do I fill my shelves with $10.00 items that I make $10.00 profit, or with $200.00 items that earn me $40.00 profit...what if the $200 items take up much more space, or vice versa...what if one of the items sits on the shelf longer. Do you have any ideas of a formula that I could use to score or grade products, allowing me to maximize my profits by replacing low scoring products with higher ones; I think the formula would need to consider:

1. Markup
2. Absolute amount of profit
3. Turnover rate (and production lead time) Suppliers take various times to deliver an order, some vendors can have an order at my door in 2 weeks, others take 90 days. With these longer delivery times, I usually order more than I need, using valuable capital and space.
4. Volume of stored inventory.

Any ideas on how to build this formula and weigh these variables?
 
Well, seems to me that you're complicating things by bringing in shipping costs;
you're really acting as an agent/collector for the shipping company: you collect
their fee from your customer, then remit to them.
I'd remove all references to shipping costs.
Geezzz....you can even charge the shipping company a "finder's fee"!

But I'm no business analyst...

Perhaps Subhotosh (a tutor here) will come up with something different
(he always does!), but I think he's got an hour left in the corner, so just
be patient...
 
I am not sure a volunteer site is the place to try to get answers for this complex a set of questions. Most of us work. Some of us are consultants and get paid to do this level of work.

Mathematical and economic models should always be treated as guidelines or suggestions because they can never take into account all the real-world factors that impinge on a real business. So, I'll give you a couple of hints. First, keep your initial models simple. Even complex ones are incomplete and more prone to error so before you add complexity, make sure the simple model is giving you good suggestions.

Second, comparing profitability by comparing gross margins (or mark-up percentages) is wrong. Example. Product A, with a sales price of $30, costs $15 and has shipping costs of $9. Unit profit = $6. Profit margin = 20%. Product B, with a sales price of $60, costs $48 and has a shipping price of $3. Unit profit = $9. Profit margin = 15%. Would you rather make $9 or $6? Of course, comparing unit profit by comparing profit margins works when sales prices are the same. However, even when unit prices are the same, unit profit alone does not allow you to compare profit contribution per period; you need to take units sold per period into account as well.

Third, as for your "drastically" better example that does involve items with identical sales price, the significance of the difference depends on the average time in stock or turnover period. If you are turning inventory over quickly, the fact that you front the money on the acquisition price and so incur interest is pretty insignificant if the period over which you are paying interest is just a day or two.

Fourth, there are stocking models that can take into account sales rates, carrying costs, costs of lost sales due to out-of-stock conditions, space constraints, etc. Some get very complex, and I have already told you my opinion of complex models.

Fifth, you MAY not be optimizing if you limit your thinking about fixed overhead to averaging it equally across products. Here is an admittedly extreme and simplified example.
Fixed Overhead = $10000.
Sales of Product A if Fully Stocked = 8000.
Unit Profit of Product A = $0.75
Sales of Product B if Fully Stocked = 2000.
Unit Profit of Product B = $4.75

Profit if both Products A and B are fully stocked)= (8000 * .75) + (2000 * 4.75) - 10000 = 6000 + 9500 - 10000= 5500

Fixed Overhead Per Unit Sold = $1.00.
So, on that basis, it looks as though you lose $0.25 on each sale of Product A and make $3.75 on each sale of Product B. Should you discontinue Product A because it is a "loser"?

Profit if only Product B is stocked = (2000 * 4.75) - 10000 = 9500 - 10000 = - 500.

The point is that Product A is contributing a lot to paying fixed overhead. The average mislead you.

As I say, I have not answered your questions. Probably you could take advantage of a simple linear programming model, a breakdown of overhead into fixed and variable components, and costing on a unit contribution basis. While that is not too involved, there is no way you are going to get that on a volunteer site.
 
Denis said:
Perhaps Subhotosh (a tutor here) will come up with something different
(he always does!), but I think he's got an hour left in the corner, so just
be patient...

Denis, how would I go about having SUBHOTOSH take a look at my post? I searched and found the ID but there wasn't an option for me to send a PM. I think I do need a linear programming model as Jeff suggested, but i want to make sure I'm headed in the right direction. Thank you both!!!
 
if you click on SK's name in any post, you will get a page that has a small PM button on it about halfway down the screen and toward the left a bit. Click it.
 
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