Direct Answer
A focused custom-software project for a service business takes 6 to 12 weeks. Internal dashboards or single-purpose tools run 4–6 weeks. Multi-user portals with auth, billing, and integrations run 10–16 weeks. Anything past 16 weeks usually means scope was unclear at kickoff.
Short version
“A focused custom software project takes six to twelve weeks. Multi-user portals run ten to sixteen weeks.”
Use 2-week sprints with a working demo at the end of each — it forces priority decisions weekly.
Lock the scope of v1 to the absolute minimum that delivers the business outcome. Phase 2 always exists.
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