Old software costs more than its licence. It ties people to screens nobody should have to fill in any more.

Licences for work no person should have to do

In many companies there is software that gets paid for and hardly anyone opens. That is the visible part. The more expensive part is the user seats that are used daily, but for one thing only: reading data from one system and typing it into another. The order from the shop into the ERP. The invoice from the inbox into accounting. The contact from the form into the CRM.

That is not carelessness on the part of the people. It is a consequence of the architecture. Software built for people at screens demands user seats even for work no person should have to do. Each of those seats costs twice: the licence and the hours of the person in front of it.

We call this the legacy tax. It appears on no invoice and grows with every year in which the business changes and the software does not.

Why this used to be right

The economist Ronald Coase explained in 1937 why companies exist: coordination inside a company is cheaper than looking for someone on the market for every task. ERP systems were the technical answer to that. They pulled orders, stock, invoicing and accounting into one place and made internal coordination cheaper. That was a good decision.

For a few years now it has only been half right. Keeping the data in one place is still correct. The work on that data no longer has to go through the vendor’s screens. A language model today reads an invoice and enters it, for a fraction of a cent. The cost of that kind of brainwork is falling. The licence per user seat is not.

What changed between 2022 and 2026

A few years ago a company processing a few hundred orders a day needed a whole team in order entry for that, plus people in accounting and data maintenance. All of them with their own seat in the ERP.

Today a layer of your own between the systems can take over that work. An interface is a technical access through which a program talks to the ERP, without a screen and without a user seat. Through such a layer, orders from the shop go straight into the ERP and invoices from the inbox straight into accounting. The ERP keeps running, but as a database, not as a workplace. The people who used to type work on what needs judgment: special cases, customer contact, planning. How to build such a layer without chaining yourself to a new vendor is in Automation Without Handcuffs.

How many user seats disappear depends on your starting point. Technical access is considerably cheaper than seats for people with most vendors. The exact terms are in your contract and that is where it pays to look.

A typical case

A machine builder plans the move to the new version of its ERP. The vendor quotes many months of runtime and a sum that makes management swallow. The reason for the move is rarely the ERP itself. It is the screens nobody wants to use any more and the workflows the old system cannot represent.

The other way: the existing ERP stays. On top of it comes a layer of your own that reads and writes the data through the interface. Sales and production get new, lean interfaces that map exactly their work. The migration is dropped or moved to a point where it no longer hurts. In projects we often see that people adopt the new interfaces without training, because they are simpler than the old screens.

Two honest limits. First, this route needs a usable interface in the old system. Very old installations sometimes do not have one or only at extra cost. Second, you then own code that you have to maintain. That is the price of it belonging to you.

Question	ERP as workplace	ERP as database
Who enters data	People through screens	Programs through the interface
What an additional process costs	New user seats	Requests to the layer
What happens at a version change	Big project, everyone affected	Layer stays, connection is adjusted
Who owns the process logic	The vendor	You

May a machine do the bookkeeping?

That is the most common question from managing directors. The answer is yes, under conditions set by the GoBD. Those are the German tax authorities’ principles for electronic bookkeeping. Three of them are decisive for automated accounting.

Traceability. Every booking by the machine is logged with the original, the reasoning and the booking number. Why cost centre 4900? It is in the log. An auditor can read years later how the decision came about. That is often more transparent than a person who no longer remembers.

Immutability. The document is archived on receipt and never touched again. The machine works with copies. Documents currently have to be kept for eight years, the process documentation for ten. The periods were shortened in 2025, so check the current state with your tax advisor.

A person keeps the responsibility. Above an amount you set, the case waits and a person decides. The same applies when the machine is unsure. Legal responsibility stays with the person, not the program.

On top of that comes the process documentation. The GoBD require a description of how your bookkeeping works technically. With automated booking that is not paper for the drawer but the proof that the three points above are met. Whether your auditor accepts the setup depends on that description. We have no statistics on tax audits and promise none. What we can say: a clean log is easier to explain in an audit than an inbox full of forwarded emails. How to think about access and security in this context is in The Firewall Is Me.

What you can decide now

Every month in which people transfer data between systems by hand costs you twice: the hours and what those people could have done instead. Competitors who have already rebuilt their workflows no longer carry that cost.

Three decisions are pending:

1. Inventory. Count the user seats that are only used for retyping and forwarding. That is your legacy tax in numbers.
2. Architecture. For every planned migration, check whether a layer of your own on top of the existing system reaches the same goal faster. Not every migration is unnecessary. Many are. How such a setup scales without new hires is in a separate article.
3. Ownership. Build the process logic yourself or have it built, but in a way that it belongs to you. The software underneath is replaceable. Your knowledge of your own workflows is not.

What you can check now

• Open the licence statement of your ERP and your CRM. Mark every seat whose holder mainly transfers data from another system.
• Ask your vendor in writing whether there is an interface, what technical access costs and what it is allowed to do.
• Take one process such as incoming invoices. Write down which decisions in it a person has to make and which not.
• Talk to your tax advisor about the process documentation before the first booking runs automatically.

If you are not sure whether your system has a usable interface, send us which ERP in which version you run. That can usually be settled in an hour.