Replenishment

When a stock spreadsheet stops working, and how to tell

Most stores start with a spreadsheet and most of them are right to. The interesting question is not whether it works, it is which change breaks it.

Marcus VolstedCo-founder, Restocio Published 6 September 2026Updated 6 September 20266 min read

When a stock spreadsheet stops working, and how to tell

A spreadsheet stops working when the decision stops being arithmetic and starts being a forecast. While you can look at a number, compare it to another number and know what to order, a spreadsheet is the correct tool and anything else is overhead. The line gets crossed when the information you need to decide is no longer visible on the day you have to decide.

That framing matters because most advice on this topic is written to sell software, so it treats the spreadsheet as the problem. It usually is not. Four specific changes break it, they break it in a predictable order, and none of them is about how organised you are.

Is a spreadsheet good enough for inventory?

Often, yes. It genuinely is the right tool when all of these hold: your supplier delivers faster than you review, you use one shipping route, you can review the whole catalogue in one sitting, and nothing significant is in transit while you decide. A store with thirty products from a domestic supplier who ships in a week fits that comfortably, and swapping in software would add work rather than remove it.

We would rather say that plainly than pretend otherwise. If the description above is your business, stop reading here.

What breaks first?

Lead time overtaking your review cycle. This is the first one and the one people misdiagnose. When goods arrive in a week, current stock tells you what to order, because the future you are ordering for is a week away and looks like today. When goods take ninety days, current stock is nearly irrelevant. You are ordering for a shelf three months from now, and the number you need is what demand will be then, not what stock is now.

A spreadsheet can hold that calculation. What it cannot do is notice when the answer changed. The deadline arrives silently, the sheet still looks fine, and the miss only becomes visible when the shelf empties eleven weeks later. That delay between the mistake and the symptom is what makes it so hard to learn from.

What breaks after that?

A second shipping route. The moment you can send goods by sea or by air, every order carries a decision about how much goes on the cheap slow route and how much has to fly. Done properly it depends on how many days of stock you have left, how long each route takes, and what each costs per kilo. That is maintainable as a formula exactly once, by the person who built it, and it silently rots the first time a rate changes.

Goods already on the water. Netting off what is already coming is easy to describe and easy to forget. Miss it and you order a second time for stock you have already paid for. Most spreadsheet double-orders trace back to this, and they are expensive twice, once in cash and once in the space it occupies.

More products than one sitting. Past a few hundred, nobody reviews every line every week. In practice you check the products you remember, which are the ones that recently caused a problem. The quiet ones go unexamined until they become loud.

How many products can one spreadsheet handle?

The count matters less than the review it demands. One number worth working out for yourself: multiply your products by the seconds it honestly takes to judge one, and see whether the total is a task you will actually do every week. Three hundred products at twenty seconds each is over an hour and a half of undivided attention, weekly, forever.

Most people do not do that. They sample instead, and sampling is fine right up until the unexamined tail is where the money is. This is the least dramatic of the four and the most common.

What should you do before switching?

Get the inputs right first, because they move with you and a tool cannot invent them. Your real lead times, measured from when you ordered to when the goods were countable, not what the supplier quoted. Your cost prices, including freight. Which supplier actually supplies each product. A tool built on guessed inputs produces confident wrong answers faster than a spreadsheet produces uncertain ones, which is a worse position to be in.

Keep the spreadsheet during the changeover, too. Running both for one ordering cycle and comparing the two answers is the cheapest way to find out whether the new inputs are right, and if the numbers disagree wildly, that is usually the inputs rather than the software.

Where Restocio fits

It is built for the store that crossed the first line and then the second, which in practice means importers. It works out the quantity from the rate each product actually sells at, nets off what is already in transit, and splits the order across sea, rail and air so the cheap route carries what it can and only genuinely urgent units fly.

It will not help a store that has not crossed those lines. A domestic supplier, one route and a short lead time is a spreadsheet problem, and we would rather tell you that than sell you a subscription you would cancel in two months.

Common questions

Is a spreadsheet good enough for managing inventory?

Yes, while the decision is still arithmetic you can do by looking. If your supplier delivers faster than you review your stock, you use one shipping route, nothing significant is in transit while you decide, and you can review every product in one sitting, a spreadsheet is the right tool and software would add work.

What is the first thing that breaks in a stock spreadsheet?

Lead time growing longer than your review cycle. With a one-week delivery, current stock tells you what to order. With a ninety-day delivery you are ordering for a shelf three months away, so current stock is nearly irrelevant, and the spreadsheet keeps looking fine while the deadline passes. The mistake only becomes visible weeks later when the product runs out.

How many products can you manage in a spreadsheet?

It depends on the review the spreadsheet demands rather than the row count. Multiply your product count by the seconds it takes to judge one line honestly: three hundred products at twenty seconds each is over ninety minutes of focused work every week. Most people start sampling instead, and the products they skip are the ones that quietly cause the problems.

Why do spreadsheets cause double orders?

Because netting off goods already in transit is a manual step that is easy to forget. Order once, forget the container is coming, order again, and you have paid twice for stock you already own and now have to store. This is the most common expensive spreadsheet error among importers.

What should I prepare before moving off a spreadsheet?

Your measured lead times from order date to the date goods were countable, your cost prices including freight, and which supplier supplies each product. Those inputs move with you and no tool can invent them. Run both systems for one ordering cycle and compare the answers, because a large disagreement is usually a wrong input rather than a wrong tool.

Marcus Volsted

Co-founder, Restocio

Marcus co-founded Restocio and works on it daily with a Swedish importer who plans their purchasing in it every working day. Restocio is built in Sweden by two founders, one Swedish and one Danish, and Marcus is the Danish one. Most of the examples on this blog come from that store's real ordering decisions rather than from a textbook. Why we are building it.