Custom App Development
We scope, build, and operate custom applications for web, mobile, and internal operations — priced as a fixed-scope project instead of an open-ended hourly estimate, and backed by a 6-month post-launch bug-fix guarantee.
Typical builds: $35,000 – $350,000 · 6 – 30 weeks · US-based senior engineers
What custom app development covers here
A custom app is software built for how your business actually runs, rather than the closest off-the-shelf tool plus the spreadsheets that grew around its gaps. In practice that means one of five things — often several of them in the same project.
Customer-facing web apps
Portals, booking flows, marketplaces, configurators, and subscription products — built with Next.js or React on a typed API, with authentication, payments, and an admin console your team can actually operate.
Mobile apps
iOS and Android from one codebase in React Native or Flutter where that is the right call, and native Swift or Kotlin where the hardware, performance, or offline behavior demands it. Store submission, push, and deep links included.
Internal tools and operations software
The scheduling, quoting, dispatch, inventory, and reporting apps that replace a stack of spreadsheets. Cheaper than customer-facing work, and usually the fastest payback because the labor cost being removed is already on your books.
AI-enabled products
LLM features, retrieval over your own documents, document and image analysis, and predictive scoring — shipped with evaluation harnesses, guardrails, and cost controls rather than as a demo that never leaves the notebook.
Also common: integrations — wiring a custom app into the accounting, CRM, payments, shipping, or EHR systems you already run, and modernizing a legacy app that works but cannot be changed safely.
What a custom app project includes
Every engagement is a fixed-scope project with the same deliverables, whether it is a six-week internal tool or a nine-month platform replacement.
- Discovery and scoping — requirements, constraints, and success criteria written down before a price is fixed
- A written fixed-price proposal with a milestone schedule, so the number matches the work
- Architecture and data model — database design, API contracts, authentication, and permissions
- Product and interface design for the screens the app actually needs, not a full design system you will never maintain
- The build itself, delivered in reviewable milestones you can use and give feedback on
- Third-party integrations including payments, accounting, CRM, shipping, and identity providers
- Testing and release engineering — automated checks, staging, and a deployment pipeline
- Handover in your own repository, with documentation, so your team is never locked out of the codebase
- A 6-month post-launch bug-fix guarantee on everything inside the delivered scope
- Optional managed hosting — monitoring, backups, and deploys run by the same team that built the app
What custom app development costs
These are the US agency ranges we price against, by product type. They are wide on purpose: "build an app" is like "build a house" — nobody can price it before they know the size, the site, and the finishes.
| What you are building | Typical build cost | Timeline |
|---|---|---|
| Internal tool or single-purpose app (login, CRUD, one integration) | $35,000 – $80,000 | 6 – 10 weeks |
| Customer-facing mobile app (iOS + Android, notifications, payments) | $70,000 – $160,000 | 10 – 16 weeks |
| B2B SaaS product (roles, admin, reporting, integrations) | $90,000 – $250,000 | 14 – 24 weeks |
| Booking or rental platform (availability, calendar, deposits) | $60,000 – $150,000 | 10 – 18 weeks |
| Two-sided marketplace (onboarding both sides, search, payouts) | $120,000 – $350,000 | 16 – 30 weeks |
| AI-enabled features (LLM workflows, retrieval, guardrails, evaluation) | +$25,000 – $80,000 on the base app | +4 – 10 weeks |
| Enterprise replacement or integration-heavy platform | $250,000+ | 6 – 12 months |
Two caveats matter more than the numbers. First, these are US agency ranges; offshore teams quote 40–60% less on paper and the gap narrows once you account for coordination, rework, and your own time. Second, the low end of each range assumes a clean scope that does not change mid-build — scope change, not code, is what breaks budgets. Read the full cost breakdown, including where the money actually goes phase by phase.
What moves a custom app quote
Two apps with the same screen count can differ by 3× in price. These are the seven factors that decide which end of the range you land on.
Third-party integrations
Each external system (accounting, CRM, payments, shipping, EHR) adds roughly $5,000–$25,000. The cost is rarely the happy path — it is the error handling, retries, and rate limits around it.
Authentication and permissions
One login screen is cheap. Multi-tenant roles, team invitations, SSO, and audit trails are a real subsystem, and a common hidden cost in B2B work.
Money movement
Split payouts, refunds, disputes, tax handling, and KYC are the difference between a $90,000 app and a $250,000 one.
Realtime and offline behavior
Live chat, presence, collaborative editing, and unreliable-network support must be designed on day one, not retrofitted later.
Data migration
Importing years of spreadsheets or a legacy database is usually underestimated by a factor of two — and it is unavoidable if the old system is being replaced.
Compliance and AI features
HIPAA, PCI-DSS, or SOC 2 readiness typically adds 15–40%. On the AI side, the model call is the cheap part: evaluation, retrieval tuning, guardrails, and latency work are the real cost.
How a custom app build runs
You always know what is being built next, what it costs, and when it lands.
Scoping call
A short call to understand the workflow, the users, the systems involved, and what success looks like. No charge, no obligation.
Fixed-price proposal
A written scope with a price and a milestone schedule. If a quote has no line for discovery, the agency is guessing — ours does not.
Build in milestones
Senior engineers build against the agreed scope and ship reviewable milestones, so feedback arrives while it is still cheap to act on.
Launch and guarantee window
Deployment, monitoring, and a 6-month window in which any bug inside the delivered scope is fixed at no extra cost.
Operate and extend
Optional managed hosting, support, and a roadmap for the next release instead of a handoff-and-disappear ending.
The stack we build custom apps on
Boring, well-supported technology chosen so that the second engineer to touch the codebase — yours or ours — is not fighting it.
- Web: React, Next.js, Node.js, TypeScript, Express
- Mobile: React Native, Flutter, Swift, Kotlin, Unity3D
- Data: PostgreSQL, MySQL, MongoDB, Redis, object storage
- AI: Python, LLM APIs, retrieval pipelines, computer vision, evaluation harnesses
- Infrastructure: AWS, Docker, CI/CD pipelines, monitoring, backups
Existing codebase already on something else? Fine — we work inside the stack you have rather than rewriting it for our own convenience. See the full list of services or look at products we have shipped.
Custom app development FAQ
How much does custom app development cost?
Usually $35,000-$80,000 for an internal tool or single-purpose app, $70,000-$160,000 for a customer-facing mobile app, $90,000-$250,000 for a B2B SaaS product, and $120,000-$350,000 for a two-sided marketplace with payments. Integration-heavy or enterprise platforms can pass $250,000. Every project is quoted as a fixed price after a scoping call.
How long does it take to build a custom app?
Roughly 6-10 weeks for an internal tool, 10-16 weeks for a customer-facing mobile app, 14-24 weeks for a B2B SaaS product, and 16-30 weeks for a two-sided marketplace. AI features add about 4-10 weeks on top of the base app.
Do you build both web and mobile apps?
Yes. Most projects are one backend serving a web application and a mobile app, so data and permissions stay in a single place. Mobile is built with React Native or Flutter from one codebase where that fits, and native Swift or Kotlin where performance, hardware access, or offline behavior requires it.
Can you work with our existing codebase or team?
Yes. We regularly extend an application another team started, integrate a custom app with accounting, CRM, payments, or EHR systems already in use, and modernize a legacy app that can no longer be changed safely. We work in the stack you already have rather than rewriting it for our convenience.
Do we get the source code?
Yes. Your project is delivered in your own repository with documentation, so your team keeps access to the codebase and is never locked out of it or dependent on 723 Studios to make a change.
What happens after launch?
Any bug inside the delivered scope is fixed at no additional cost for six months after launch. After that, managed hosting, monitoring, backups, and ongoing development are available on a support plan.
Scope your app before you price it
Send the workflow you want to replace and we will come back with a fixed-scope proposal, a price, and a schedule — not an hourly estimate that moves.