Spring Boot 3.5 EOL Migration Calculator: Estimate Your Upgrade Timeline to Spring Boot 4

Spring Boot 3.5 end-of-life is approaching, and for many teams the biggest unknown isn’t whether to migrate — it’s how long the migration will actually take.

This Spring Boot 3 → 4 Migration Calculator helps you estimate the real-world effort required based on application size, dependencies, team capacity, and mandatory platform upgrades, so you can plan ahead before Spring Boot 3.5 reaches end of life.

For what the estimator is, how to use it, and why it matters as Spring Boot end-of-life approaches, click here to learn more.

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Frequently Asked Questions

How long does it take to migrate from Spring Boot 3.5 to Spring Boot 4?

The time required to migrate from Spring Boot 3.5 to Spring Boot 4 varies widely based on application size, dependency usage, test coverage, and team capacity. For many production applications, migrations can take anywhere from several weeks to multiple months rather than being a simple version upgrade.

What factors affect the duration of a Spring Boot 3 to Spring Boot 4 migration?

Migration timelines are influenced by the number of applications involved, codebase complexity, use of Spring projects such as Data, Security, or Cloud, required JDK and container upgrades, testing effort, and whether automated tools like OpenRewrite are used.

What changes are required when upgrading to Spring Boot 4?

Spring Boot 4 introduces mandatory platform upgrades including newer Java versions, updated servlet containers, Hibernate upgrades, Jackson 3, newer testing frameworks, and the removal or replacement of unsupported components such as Undertow. These changes often require code updates and extensive testing.

What happens when Spring Boot 3.5 reaches end of life?

After Spring Boot 3.5 reaches end of life, it no longer receives official security patches or bug fixes. Newly discovered vulnerabilities remain unpatched, increasing security risk, compliance challenges, and the likelihood of emergency migrations.

Is migrating from Spring Boot 3.5 to Spring Boot 4 just a dependency upgrade?

No. While version changes are involved, migrating to Spring Boot 4 typically requires addressing breaking changes, platform upgrades, dependency compatibility issues, and test failures. Treating the migration as a simple dependency bump often leads to unexpected delays and risk.

Does Spring Boot 4 require a newer Java version?

Yes. Spring Boot 4 requires newer Java baselines, typically involving upgrades beyond Java 17. Many teams must plan staged JDK upgrades to ensure compatibility and stability before completing the migration.

Which Spring projects are most impacted by Spring Boot 4 upgrades?

Projects commonly affected include Spring Data, Spring Security, Spring Cloud, Spring Web, Spring Batch, and Spring Integration. Each additional Spring module increases migration complexity and testing requirements.

Can automated tools like OpenRewrite reduce Spring Boot migration time?

Automated refactoring tools such as OpenRewrite can significantly reduce manual effort by handling repetitive code changes. However, they do not eliminate the need for manual validation, testing, and production readiness checks.

What are the biggest risks when migrating to Spring Boot 4?

Common risks include test failures, dependency incompatibilities, production regressions, performance changes, and security gaps caused by rushed upgrades. Platform-level changes often represent the largest source of unexpected effort.

What are my options if I can’t migrate before Spring Boot 3.5 EOL?

If migrating before end of life is not feasible, organizations can use commercial end-of-life support to continue receiving security patches and vulnerability remediation while planning a Spring Boot 4 upgrade on a safer, business-aligned timeline.

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