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The Solo 401(k) Calculator helps self-employed individuals and freelancers calculate their maximum retirement contributions. Based on 2025 IRS limits: employee deferral $23,500, catch-up $7,500, total limit $70,000. All calculations run locally in your browser β your data stays private. Supports Sole Proprietor, S Corp, C Corp, and Partnership entities. Simple, instant results. Built with pure front-end technology for speed and security.