How much does an API integration cost?

What does an API integration cost? The short answer

An interface is not an off-the-shelf product but connects two or more specific systems. The price therefore depends mainly on what those systems can do: if the target software offers a modern, documented REST API with test access, the connection is often manageable. If you have to work with legacy systems, file exports or patchy documentation, the effort rises.

What is to happen with the data is equally important. A connection that exports orders once a day is simpler than a real-time synchronization of products, prices and stock levels in both directions. In our experience, a large part of the effort lies not in the actual connecting but in reconciling data formats and handling error cases.

The cost factors of an interface in detail

It starts with the analysis: which data is transferred, which system is the leading one, how are duplicates and conflicts handled? This produces a data mapping – that is, the assignment of which field in system A corresponds to which field in system B. With products with variants, customers with multiple addresses or different tax rates, this quickly becomes demanding.

Then follow implementation, authentication, tests with real data, logging and notifications on errors. Do not forget: interfaces have to be maintained. If a provider changes its API or introduces a new version, adjustments are needed. So plan the maintenance from the start instead of clarifying it only at the first outage.

• Number and type of connected systems
• Data direction: one-way or bidirectional
• Frequency: real time, hourly or daily
• Data mapping and special cases
• Error handling, logs and monitoring
• Maintenance when APIs change

What does a DATEV interface cost?

With a DATEV interface (DATEV is the accounting software and data platform widely used by German tax firms), the routes differ considerably. The simplest is an export in DATEV format that your software generates as a file and your tax firm imports. A direct online connection via the interfaces DATEV provides for software vendors is more complex; depending on the use case, registration and certain approvals are required.

Costs also depend on which data is handed over – such as booking entries, receipt images or master data – and how close the coordination with your tax firm has to be. Clarify in advance with your tax advisor which format and handover route work best for them. That way you avoid an interface that nobody at the tax firm uses.

What does e-invoicing software cost – and when is an interface worthwhile?

There are two routes for e-invoices. Many accounting and invoicing programs can already generate and receive e-invoices; the costs then consist mainly of license or subscription fees. If your invoices, on the other hand, originate in your own software, a shop or an inventory management system, an interface that generates structured formats such as XRechnung or ZUGFeRD directly from your data makes sense.

Since January 1, 2025, domestic businesses in Germany must be able to receive e-invoices in the B2B sector; the obligation to issue them is being introduced with transition periods until 2027 and 2028, respectively. Which solution is cheaper depends on invoice volume and the number of systems involved. Our guide on the e-invoicing obligation explains the details; this note does not replace tax advice.

Ready-made connector, automation or custom interface?

Not every connection has to be programmed from scratch. For widespread systems there are ready-made connectors or plugins, for example between shop systems and inventory management. Automation tools such as n8n connect many services with little custom development. That saves entry costs but often brings ongoing fees and limits for special cases or large data volumes. In addition, your data then also sits with another provider.

A custom interface is worthwhile if your processes deviate from standard solutions, large volumes of data must be processed reliably or you do not want to depend on additional third-party providers. In the initial consultation, we check whether an existing connector is enough or a custom solution is more economical – even calculated over several years. Sometimes a combination also makes sense: a standard connector for the normal case, custom logic for the special cases.

How we calculate your interface

At Nano Concepts, we develop interfaces to DATEV, SAP, EDI partners, Shopware and other systems, as well as e-invoicing solutions. It starts with a short analysis of the systems involved, data flows and special cases. After that you receive a transparent quote, preferably at a fixed price for a clearly defined scope – including a recommendation for later maintenance.

For orientation: manageable connections to a well-documented API can fall within our Starter package from €2,500. Bidirectional integrations of several systems tend to fall into the Professional package from €8,000, and we calculate large integration projects individually as Enterprise. The exact quote follows after the free initial consultation. Ongoing fees of the connected providers are not included.