As of May 2026

API & Integration Development Costs: Transparent Calculator

Calculate the costs for API development and system integration with our interactive calculator. A medium-complexity connector for two systems typically starts from approx. €9,100 excl. VAT.

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

API and integration development costs grow with endpoints, auth, load, and documentation.

API scope compared

Internal admin API
Public partner API with SLA and versioning
Contract tests, staging, and operations

See API development service and the API integration ROI calculator.

API cost calculator

What does your API cost?

Calculate the cost of API development and system integration

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What do you want to implement?

API & Integration Development – Cost Overview (JavaScript required)

Typical costs: Simple REST API integration from approx. €2,100, custom API development from approx. €5,600, complex multi-system integration from approx. €14,000 (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

€2,100 – 7,000 excl. VAT

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

Typical

Custom API Development

€7,000 – 21,000 excl. VAT

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

Enterprise Integration

€21,000 – 70,000+

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.

API Development Costs

Costs & budget

How much does a simple API integration cost?

Integrating two systems with standard REST APIs costs €2,100 – 5,600 excl. VAT. More complex integrations with data mapping, error handling and logging: €7,000 – 17,500 excl. VAT.

How much does custom API development cost?

Own REST or GraphQL API from approx. €5,600 excl. VAT for simple CRUD. Full business APIs with authentication, rate limiting and documentation: €10,500 – 28,000 excl. VAT.

What influences integration costs most?

Mainly the target system's API quality: well-documented REST APIs with sandbox are cheaper. Further factors: data mapping complexity, error handling and security requirements.

Björn Groenewold – Geschäftsführer Groenewold IT Solutions

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Technology & methods

REST, GraphQL or webhooks – what is right?

REST for standard CRUD and classic integration. GraphQL for flexible queries. Webhooks for real-time events – we often combine several approaches.

Can legacy systems without APIs be integrated?

Yes – via database access, file exchange (CSV, XML, EDI), screen scraping/RPA or middleware. Effort is higher than with modern APIs but feasible.

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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 – depending on API quality and test environments.

What should we consider for ongoing interface maintenance?

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

Security & documentation

How do we secure APIs against unauthorised access?

OAuth 2.0 / API keys with rotation, rate limiting, TLS for all connections and access logging. For sensitive integrations: IP whitelisting and mTLS.

What documentation do we receive after API development?

OpenAPI/Swagger specification, technical interface manual, operations guide with error handling and runbooks for support – documentation is part of the project.

How do we test interfaces before go-live?

Unit tests for transformation logic, integration tests against staging, load tests for critical interfaces and chaos tests (timeouts, faulty payloads) in the CI/CD pipeline.

More about API development

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

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.

The calculator result for Api Development is indicative only – a binding budget follows scope alignment, data review, and quality targets.

Plan follow-on costs

Operations and maintenance separate from the initial build
Internal key users and training
Monitoring and support after go-live

Next steps after the calculator

Intro call: funding and phased delivery
Discovery, pilot, or rollout matched to risk
Documented assumptions and exclusions in the quote

Compare related calculators in the costs hub for edge cases (integrations, compliance, parallel run).