A few days ago, I was speaking with a friend of mine — an Amazon seller who runs a sizeable business and tries to follow his restock recommendations as closely as possible. At some point he said something that I've heard many times:
"I stick to the recommended stock levels. Tools tell me what's 'healthy', how fast products sell, and when I need to reorder. I try not to hold anything longer than 60 days — that's what everyone advises."
This immediately reminded me of similar discussions I had years ago with teams in large e-commerce companies. Different contexts, same underlying assumptions. And these assumptions often lead to financially inefficient choices.
Now let me explain why.
How Traditional Restock Tools Work And What They Assume
Most restock tools follow the same logic:
- Define a recommended inventory level.
- Estimate how fast this inventory will be consumed.
- Factor in lead time to calculate reorder dates and quantities.
- Aim to avoid stockouts and excessive storage.
In other words, their implicit objective is to keep the target inventory turnover.
Operationally, this makes sense:
Buy and hold what sells, at approximately the rate it sells.
But this logic has built-in limitations that become visible once you look at inventory through a financial lens, not only an operational one.
Where This Approach Breaks: Identical Rules For Fundamentally Different Products
Here's a simple question.
Which product is "better"?
- •Product A, which stays in stock for 30 days on average,
- •Product B, which stays for 90 days?
Most people (including my friend) would say: Product A, because it turns faster.
But what if Product B generates ten times more profit per unit, even after storage fees? Suddenly, the comparison is no longer straightforward.
If you had to invest in only one of them assuming you have capital constraints, which SKU should receive your capital?
This is where many sellers realize that the standard operational logic doesn't answer the financial question.
Clear Answers Exist Only In One Simple Case
The decision is obvious only when one product is better on both dimensions. If A turns faster and has higher margin — A is better. But the moment one product turns faster while the other has higher margin — which is exactly what happens in real life — the comparison becomes non-trivial.
You cannot say which SKU is "better" until you understand how margin and turnover interact. This interaction is precisely what operational tools tend to ignore.
What About ABC Analysis? Doesn't It Solve This?
More experienced sellers sometimes say:
"We already use ABC analysis. That's how we categorize products and decide what deserves attention."
That is true. ABC analysis or ABCXYZ analysis is a legitimate and useful tool. It helps identify the small group of products that contribute the most to the business. It's a structured way to focus on what matters.
Nevertheless it has a fundamental limitation that often goes unnoticed:
ABC analysis ranks products across the entire catalog, but it doesn't help you choose between products within the same class.
And this is where the real decisions happen.
Inside class A, for example, you may have two great options:
- •a faster-turning SKU with lower margin,
- •a slower-turning SKU with higher margin.
ABC analysis puts both into the same "high-priority" category — but it does not tell you which one deserves the next euro of investment when your budget is limited.
That final step — choosing between strong products with different turnover-margin profiles — is exactly where sellers need to evaluate the two options within one class.
This is the step ABC cannot perform.
The Core Problem: Margin And Turnover Are Evaluated Separately
Here is the issue I see repeatedly:
Turnover is treated as an operational metric.
Margin is treated as a financial metric.
And restock decisions rarely connect the two.
Margin without turnover tells you nothing about how effectively your capital works. Turnover without margin tells you nothing about the value created when the product is finally sold.
Most restock tools:
- •show margins,
- •but do not use them as a basis for recommendations.
Margins appear only as a reference, not as a deciding factor.
The restock tools optimize for stock availability and storage costs — not for capital allocation.
The result is predictable: they tell you what to reorder, but not whether that product is actually the best use of your money.
The better approach for replenishment decisions is to evaluate the joint contribution of margin and turnover to ROI and overall capital efficiency. In other words, to understand both profit and the speed at which investment in working capital returns covering your cost of capital.
Why Relying On "Universal Rules" Leads To Hidden Risks
Because tools and classifications don't connect margin and turnover, many sellers fall back on simple rules:
- •"Don't let items sit more than 60 days."
- •"Slow movers are risky."
- •"High-margin products are always better."
These rules are well-intentioned, but they are:
- •generalized,
- •empirical,
- •and not tailored to your specific SKU economics.
It is important to remember, that such rules can be helpful, but until they replace thinking.
Sellers shouldn't forget to ask essential questions:
- •Is the fast-moving SKU actually the best place to put capital?
- •Does this product generate enough value to justify a longer cycle?
- •What is the actual financial trade-off between margin and turnover?
Once you start asking these questions, you quickly realize that many "slow" SKUs are extremely attractive — and many "fast" SKUs are efficient operationally but not financially.
The Bottom Line
The conclusion I shared with my friend, and have shared many times with e-commerce teams is simple:
Margin and turnover only make sense when evaluated together.
Separately, each metric is incomplete.
Together, they show which products truly create value.
Restock tools help manage operations, but operational efficiency is not the same as financial efficiency.
And when capital is limited, the real question is not "What should I reorder to stay in stock?" but "Where should I invest my money to create the most value?"
In the next article, Lead Time as a Financial Variable: Why Buying "Cheaper" Can Cost You More, we'll look at why lead time, often treated as a purely operational parameter, is actually a major financial variable in capital allocation decisions.