Can legacy systems be integrated?

Yes, via database access, file exchange, RPA, or middleware – higher effort than modern APIs.

What should be considered for maintenance?

APIs change (breaking changes), auth expires – monitoring and maintenance contract recommended.

What influences costs the most?

API quality of the target system, documentation, data mapping complexity, and security requirements.

As of April 2026

API & Integration Development Costs: Transparent Calculator

Q: How much does a simple API integration cost?

€3,000–8,000 excl. VAT for standard APIs, €10,000–25,000 excl. VAT for more complex integrations with data mapping.

Q: How much does custom API development cost?

From €8,000 excl. VAT for simple CRUD APIs, €15,000–40,000 excl. VAT for complete business APIs with auth and documentation.

Q: How long does an API integration take?

1–2 weeks (simple), 4–8 weeks (medium), 2–6 months (enterprise).

Q: REST, GraphQL, or Webhooks?

REST for standard CRUD, GraphQL for flexible queries, Webhooks for real-time events.

Calculate the costs for API development and system integration with our interactive calculator.

API & Integration Development Costs – What Does Your Integration Cost?

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API & Integration Development – Cost Overview (JavaScript required)

Typical costs: Simple REST API integration from approx. €3,000, custom API development from approx. €8,000, complex multi-system integration from approx. €20,000 (excl. VAT). Enable JavaScript for an interactive calculation.

Tip: Is the API integration worth it?

Calculate how much manual data management really costs you – and when automation pays off.

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API & Integration Pricing Overview

The costs for API development depend on complexity, number of systems, and API quality.

Standard Integration

€3,000 – 10,000 excl. VAT

Connect 2 systems
Well-documented APIs
Standard data formats
1–2 weeks development

Typical

Custom API Development

€10,000 – 30,000 excl. VAT

Custom REST/GraphQL API
Authentication & security
Documentation & tests
4–8 weeks development

Enterprise Integration

€30,000 – 100,000+

ERP/CRM integration
Middleware platform
High scalability
2–6 months development

What Influences Integration Costs?

The most important cost factor is the API quality of the target system. Well-documented REST APIs with a sandbox environment are inexpensive to integrate. Poorly documented or proprietary APIs significantly increase the effort.

Other factors: data mapping (how different are the data structures?), error handling (what happens during outages?), and security(OAuth, API keys, certificates?).

REST API vs. GraphQL vs. Webhooks

REST APIs are the standard for most integrations. Easy to understand, well-documented, broad support. Ideal for CRUD operations and classic system integration.

GraphQL is suited for complex data queries and mobile apps. More flexible than REST, but higher development effort. Recommended when clients need different data subsets.

Webhooks for real-time events: the target system automatically notifies you of changes. Often combined with REST for bidirectional communication.

Legacy Systems Without API

Not every system has a modern API. For legacy systems, there are still integration options:

Direct database: DB access (with caution!)
File exchange: CSV, XML, EDI via shared folder or SFTP
RPA/Screen scraping: UI automation as a last resort
Middleware: Custom API layer in front of the legacy system

Benefits of Professional API Integration

Automation

Data flows automatically between systems – no more manual transfers.

Data Consistency

Unified data across all systems through real-time synchronization.

Efficiency

Faster processes through seamless system connections.

Everything About API Development Costs

Costs & Budget

How much does a simple API integration cost?

A simple integration of two systems with standardized APIs (e.g., REST) costs between €3,000 and €8,000 excl. VAT. More complex integrations with data mapping, error handling, and logging run €10,000–25,000 excl. VAT.

How much does custom API development cost?

Development of a custom REST or GraphQL API starts at around €8,000 excl. VAT for simple CRUD operations. Complete business APIs with authentication, rate limiting, and documentation run €15,000–40,000 excl. VAT.

What influences integration costs the most?

The most important factor is the API quality of the target system. Well-documented REST APIs with a sandbox are inexpensive. Other factors: data mapping complexity, error handling, and security requirements.

Björn Groenewold – Managing Director Groenewold IT Solutions

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Technology & Methods

REST, GraphQL, or Webhooks – what is right?

REST for standard CRUD operations and classic integration. GraphQL for complex, flexible queries. Webhooks for real-time events. Often multiple approaches are combined.

Can legacy systems without API be integrated?

Yes, via database access, file exchange (CSV, XML, EDI), screen scraping/RPA, or middleware solutions. The effort is higher, but feasible.

Thorsten Frieling – Project Manager Groenewold IT Solutions

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Let us talk about your system landscape – we will find the optimal integration strategy.

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Process & Maintenance

How long does an API integration take?

Simple integrations: 1–2 weeks. Medium projects: 4–8 weeks. Complex enterprise integrations: 2–6 months. API quality and test environments are decisive.

What should be considered for ongoing maintenance?

APIs can change (breaking changes), authentication expires, data formats change. We recommend monitoring, automated tests, and a maintenance contract.

More About API Development

API Projects Are Often Eligible for Funding

API development and system integration are eligible digitalization projects. Check with our calculator which funding programs are available to you.

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Connect Systems Intelligently

We analyze your system landscape and develop the optimal integration strategy.

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Typical pricing models (overview)

Comparison: typical pricing models for software and IT projects
Model	When it fits	Budget & flexibility	Typical risks
Fixed price (fixed scope)	Clearly defined scope, stable requirements, repeatable delivery.	Predictable total cost; little room for change without a change order.	Scope creep leads to change orders or quality trade-offs.
Time & Material	Discovery, legacy, evolving requirements, or close collaboration.	Maximum flexibility; budget transparent via hourly or daily rates.	Without prioritisation, effort can grow—backlog and reviews matter.
Retainer / maintenance package	Ongoing operations, updates, small features, and support.	Agreed capacity per month; predictable follow-on cost.	Large changes may still need a separate estimate.
Hybrid (milestone + T&M)	MVP or phased releases with clear go-lives, then iterate.	Core delivery fixed price; extensions on a time-and-materials basis.	Define contractually what is in scope vs. extra work.

Calculators on this page provide indicative ranges; we choose the right model with you based on risk, scope, and planning horizon.

Costs & next steps

API and integration development costs: transparent calculator – REST, GraphQL and custom connectors.

The ranges shown are indicative. For a binding quote we discuss scope, priorities and funding options in a free intro call. Many digitalization projects qualify for grants – try our funding calculator.

Browse all cost calculators, explore services and typical solutions. Questions about Api Development? Contact us.