Custom Software Development Timeline: What 6, 12, and 20 Weeks Actually Buy You

How long does it really take to build custom software? Agencies dodge this question until the contract is in front of you, when the answer is conveniently always "longer than we said."

We publish concrete numbers up front. Here is what 6, 12, and 20 weeks actually buy you in 2026.

What 6 weeks gets you

A focused, single-purpose tool used by one team. Examples we have shipped in 6 weeks:

A CRM for a 12-person sales team replacing HubSpot + 3 spreadsheets

A custom procurement portal with 5 vendors, 4 user roles, approval workflows

A patient intake system with HIPAA-compliant forms and EHR integration

A multi-vendor marketplace MVP with Stripe Connect and 8 product categories

A field-service dispatch app with mobile schedule, photo uploads, customer SMS

The pattern: 1–3 user roles, 5–12 core pages, 2–5 integrations, single data model. The team using it is 5–50 people. Work fits one team's workflow, not multiple departments.

What gets cut from 6-week scopes: nice-to-have second user types, advanced analytics, complex permission matrices.

What 12 weeks gets you

Cross-functional platforms spanning multiple teams. Examples:

A 40-feature ERP for a 70-person logistics company (inventory + accounting + dispatch + customer portal)

A multi-tenant SaaS MVP with 4 customer types, full billing, admin dashboard, partner API

A healthcare appointment platform with provider scheduling, patient app, insurance verification, billing

An education platform with student/teacher/admin roles, course authoring, video, quizzes, certificates

A custom warehouse management system with mobile scanner, picking optimisation, carrier integrations

The pattern: 4–8 user roles, 20–40 pages, 8–15 integrations, multi-tenant or multi-team data architecture. Real complexity, but still focused — one business, not a platform for many businesses.

What 20+ weeks gets you

Enterprise platforms with deep compliance, multi-business, or scale requirements:

A SaaS platform supporting 50–500 customer accounts with white-label, custom domains, multi-region

A regulated platform requiring SOC 2 audit, HIPAA BAA, GDPR data residency

A migration of a legacy system serving thousands of daily users (data migration alone is often 4–6 weeks)

Custom AI agents with RAG over proprietary data, evaluations, fine-tuning, voice integration

The pattern: 10+ user roles, 50+ pages, 20+ integrations, dedicated platform engineering work for scale and reliability.

4 things that always extend timelines

Discovery debt. "We weren't sure exactly what we wanted" caught at week 3. Catch it at week 1 with a fixed-scope document.

Data migration from legacy systems. Especially when the old data isn't clean. Always budget 2–4 weeks more than the spreadsheet suggests.

Third-party integration delays. Stripe takes a day. ADP takes a month. Each integration's quirks matter; ask up front.

Compliance work. SOC 2 audits, HIPAA BAAs, payment-processor approvals — calendar weeks of waiting on external parties.

3 things that take less than expected

Branding and polish. A senior designer can polish a working app in 3–5 days. Don't budget a month.

Cross-browser and device testing. Modern stacks handle 90% automatically. Budget days, not weeks.

Performance optimisation. Most apps don't need it. Scope it from day 1 if they do.

How to evaluate a timeline estimate

Ask the agency three questions:

"What's in your 'out of scope' list?" — If they don't have one, the estimate is fiction.

"Show me a 6-week project similar to mine." — If they can't, you're paying for their first attempt.

"What does your weekly demo cadence look like?" — If they go dark for months, run.

If you want a fixed timeline with a fixed quote for your specific scope, our cost calculator runs 5 questions and gives both. Or contact us for a 48-hour scope conversation.