An ERP costing more than €100,000 a year, a planning tool costing €200,000, an MRP run that takes all night. And in the morning, the planner opens Excel. We see this on almost every industrial site we visit, large groups included. Production planning in Excel is not a leftover from the past that the ERP has yet to erase: in most SMEs, it is the tool that actually makes the plan.
Why does Excel hold out? What does it do better than the ERP, and where does it break? Above all, how do you move to software without losing the rules that have built up in the workbooks? This article answers with real cases.
Why production planning in Excel outlives the ERP
ERP systems structure data and flows: items, bills of materials, stock, sales orders, manufacturing orders, purchasing. That is their strength. But planning, in the sense of deciding what to make tomorrow with the material and hours available, often remains on the sidelines. Four situations we have met in the field illustrate this.
An MRP that proposes orders you cannot run
In a food company that spends more than €100,000 a year on its ERP, the MRP run takes several hours every night. In the morning, the scheduler extracts all the manufacturing orders created into Excel and checks, one by one, whether they can be run with the raw materials available. Most cannot: MRP plans at infinite capacity and ignores the material actually on hand that day. The scheduler then edits the orders by hand to balance material.
A planning tool too slow to iterate
On another site, €200,000 was spent on a planning tool. The objective is the same: material balance. With every change to the table, a screen recalculates load and capacity. The calculation takes 10 seconds. That sounds acceptable, except that the planner iterates about a hundred times a day to balance production: several minutes of waiting every day, added up, watching an hourglass. He went back to Excel, where recalculation is instant, despite the extractions and maintenance this involves.
A level of detail the ERP cannot reach
In a sauce factory, scheduling has to be accurate to the minute: prepared sauces have a very short life before packing. The ERP plans correctly, but does not go down to that level of detail. Developing the feature would be slow and expensive. An Excel workbook full of macros took over, and the teams handle last-minute adjustments themselves.
Planning pushed into the background
A biscuit manufacturer invests heavily in an ERP. As often happens, priority goes to stock, sales orders and logistics; planning is out of scope. With no tool, the team plans in Word. Elsewhere, a site balks at the cost of migrating its Sage ERP, keeps an old version and supplements it with Excel: costs are contained, but people have to juggle several tools, with the errors and maintenance that brings.
What Excel does well
These cases have one thing in common: Excel wins because it lets the planner apply their own rules, straight away.
- Instant recalculation. Change a quantity and see projected stock or remaining material move without waiting. That is what makes it possible to iterate a hundred times a day.
- Business rules in the columns. A “target cover” column, a “material consumed” column, a formula that takes the maximum of actual sales and forecasts: every site has its own, and each fits in a formula.
- Freedom of granularity. By the minute for sauces, by the week for a master production schedule, in the same workbook if needed.
- Almost zero cost to try. Testing a planning method in Excel takes a few days; in the ERP, a project of a few months.
Where Excel breaks
The same strengths become weaknesses as soon as the workbook becomes the official tool.
| What Excel allows | What it costs day to day |
|---|---|
| Extracts copied and pasted from the ERP | Re-keying every morning, stock figures out of date by midday, orders recreated by hand in the ERP |
| Formulas and macros written by one person | Dependence on its author: holidays, sick leave or departure, and the file has no one at the controls |
| A workbook that grows with the number of items | Heavy files, slower recalculation, crashes |
| Total freedom of input | Silent human errors: an overwritten cell, a partial sort, a shifted formula |
| One file per user | No simultaneous working, no history, no traceability of decisions |
An Excel update can even break a macro that had worked for months. That is why we always ask for a new version to be tested before it is rolled out on the planner's computer, and for life after Excel to be considered from the start of the project.
Replace Excel with the ERP, or keep the rules and change the container?
The question “should we replace Excel with the ERP?” is the wrong question. In the cases above, the ERP had already had its chance and did not take it, not out of ill will, but because its planning limitations are structural: an MRP at infinite capacity, an imposed granularity, long recalculation times, a configuration frozen by the implementation project. What must be kept is not the workbook, it is the rules it contains. Here is the approach we follow.
- List the rules. Write down each calculated column of the workbook and the question it answers: “how many days of cover”, “what material is left”, “which order is urgent”. That is the functional requirements specification, and it already exists.
- Separate data from decisions. Data (stock, sales orders, manufacturing orders, bills of materials) should come from the ERP automatically, every morning. Decisions (quantities, dates, priorities) stay with the planner.
- Choose a tool where columns can be programmed. If the software cannot express the rule “maximum of sales and forecasts until 10:00, actual sales only after that”, the planner will go back to Excel.
- Keep the ERP as the master. The planning tool proposes; manufacturing orders and purchases are created or updated in the ERP, with no re-keying.
- Run both in parallel for a few weeks, compare, then switch off the workbook.
What we see in the field with Excel planning
We have built planning workbooks used six days a week, from 7:00 to 19:00, for more than two years, by planners with average Excel skills. They held up because the rules were the planners' own and recalculation was immediate. They suffered every time the file's author could not be reached, or a wrong move blocked a macro. We describe one of them in this medium-term planning case in the food industry.
We also see that a planner who iterates a hundred times a day does not need a solver: they need to see instantly the effect of every change on material, load and projected stock. That is exactly what Excel gave them, and it is what planning software must give back to them, with up-to-date data, several users and a history on top.
Conclusion: keep the rules, change the tool
ERP planning limitations are real, and production planning in Excel is their logical consequence, not an anomaly. Excel does well what the ERP does badly: recalculate quickly, according to the site's rules. It breaks on what the ERP does well: shared, up-to-date, traceable data. The sensible way forward is neither to force the ERP nor to keep the workbook, but to carry the rules over into a tool that reads the ERP and leaves the planner to decide.
That is the idea behind Planiprod : your Excel rules become programmable columns, each explained in one click, fed every morning by your ERP or by your existing workbooks; the ERP stays in charge of manufacturing orders and purchasing. We explain on our page on moving from Excel to software how we take over an existing workbook, and you can request a demo with your own file.