How long will my upgrade take in calendar weeks?

Calendar time, not effort time. Most upgrades fit one of these buckets:

• 2.4.8 → 2.4.9 patch hop: 1–2 weeks. Mostly composer + reindex + smoke-test. Best done in a planned maintenance window.
• 2.4.6 → 2.4.9 minor jump: 3–5 weeks. Two minor versions of deprecation work, full UAT cycle.
• 2.4.4 → 2.4.9 multi-minor: 5–8 weeks. The PHP 8.1 → 8.3 hop kicks in here, plus several waves of extension audits.
• 2.4.0 → 2.4.9: 8–12 weeks. Composer 1 → 2, OpenSearch migration, layout-XML schema cleanup, library deprecations.
• 2.3.x → 2.4.9: 12–20 weeks. Effectively a re-build. PHP 7 → 8.3, full Knockout audit, every extension re-validated, often a Hyvä migration tagging along.

Timeline multipliers: B2B in scope adds 30–50%, multi-store adds N × 1 week per storefront, ERP integration adds 2–4 weeks for the schema-handshake retest. The calculator’s timeline output is the realistic elapsed time including UAT, not just dev hours.