# Build a SaaS plus mobile app > A SaaS plus mobile app is one product with two front doors: a browser app and a phone app that share accounts, data and billing. Build the shared back end first, then the screens. ErdiBuilds is an open marketplace where clients post app, SaaS, website and game projects, see which independent developers from the EU fit best based on what they have already built, and pay per milestone. Canonical: https://erdibuilds.app/build/saas-plus-mobile-app Last updated: 2026-11-06 (November 6, 2026) ## One product, two apps Customers sign in once and see the same data on the laptop and on the phone. Think of a coaching platform where coaches work in the browser and clients use the phone, or a field service tool with a dashboard in the office and a checklist app on site. This setup has more moving parts than a single app, so it pays to decide early which parts live where. The browser side often handles setup, reports and billing. The phone side handles quick daily actions, notifications and offline use. Compare it with a plain [SaaS](https://erdibuilds.app/build/saas) and a plain [mobile app](https://erdibuilds.app/build/mobile-app) to see what you really need. ## The shared back end is the foundation Both apps talk to the same API (A set of rules and addresses that lets one program ask another for data or actions.). If that layer is clean, a second app is mostly screens. If it is not, every feature is built twice. - One login system for both apps, for example Supabase (An open source backend with a Postgres database, user login and file storage.) or Firebase (Google's backend service with a database, login and push messages.). - One database with permission rules, such as Row Level Security (A database feature that decides row by row which user may read or change which data.). - One billing setup. If people can buy inside the phone app, the store billing rules of Apple and Google may apply, so ask your developer to check them for your case. - Push notifications (Short messages the app can send to a phone, even when the app is closed.) sent from the back end. ## Typical technologies A popular combination is Next.js (A React framework that renders pages on the server and in the browser, with routing and API routes built in.) for the browser and React Native (A framework from Meta that builds iPhone and Android apps from one JavaScript or TypeScript codebase.) with Expo for the phone, because both use TypeScript and can share types and logic. Flutter (A framework from Google that draws its own interface and builds iPhone and Android apps from one Dart codebase.) or native Swift (Apple's programming language for native iPhone and iPad apps.) and Kotlin (A programming language for native Android apps, fully supported by Google.) work as well. [Find My Stack](https://findmystack.app/?project_type=saas-plus-mobile-app) can suggest a fit for your idea. ## An example plan in milestones Many teams ship the browser app first and the phone app second. Each milestone is funded before work starts and runs 1, 2, 3, 4, 6 or 8 weeks. Milestones are from 50 to 2,000 each in your project currency. 1. For example, weeks 1 to 3, shared base: data model, login, permissions, API and a first deploy. 2. For example, weeks 4 to 7, browser app: the core workflow, account settings and the plan and billing pages. 3. For example, weeks 8 to 11, phone app: sign in, the three or four actions people do daily, notifications, a test build for a small group. 4. For example, weeks 12 to 13, release: store submission, production monitoring, support emails and a handover note. The weeks are for illustration. Developers set the length of each milestone in their proposal, and each real milestone runs 1, 2, 3, 4, 6 or 8 weeks. It is normal to hire one developer for the whole project. You can also start with one and add a second for the phone app later, as long as the API is documented. ## What belongs in the project description - Which tasks happen in the browser and which on the phone, in a simple table or list. - Whether the phone app must work offline and what must sync. - Who pays and where: on your website, in the app stores or both. - The roles in the product, for example admin, member and guest. - Platforms for the phone app and the browsers you must support. - Which version ships first, and what the second can wait for. ## How to recognise a suitable developer Look for someone who has built both a web back end and a published phone app, or a pair of developers who say clearly who owns the API. Ask how they keep the two apps from drifting apart, how updates reach old app versions and how they test sign in on a real phone. Each proposal has a match score (A number from 0 to 100 that shows how well a developer fits your project, with plain reasons such as shared technologies, similar past work, budget fit and availability.). A developer needs at least 40 to apply, and 80 or more earns a Top match badge. Technologies are listed as Expert in (up to 6) or Also works with, which tells you how deep the experience goes. Developers are independent professionals, not our employees. ## Frequently asked questions ### Should I build the browser app or the phone app first? Usually the browser app, because it ships faster and needs no store review. Build the API so the phone app can follow without changes to the base. ### Do I need one developer or two? One developer with both skills keeps things simple. Two can work in parallel once the API exists. Either way, keep all code in repositories under your own account. ### Can both apps share code? Partly. With TypeScript on both sides, types, validation and business rules can be shared. Screens are usually separate because phones and browsers behave differently. ### Do app store rules affect my subscriptions? They can. The stores have rules about selling digital goods inside apps. Ask your developer to read the current rules for your case before you design the sign up flow. ### How do I pay for a bigger project like this? Per milestone. Each milestone is funded before work starts and runs 1, 2, 3, 4, 6 or 8 weeks. A larger project is simply a series of milestones, each approved before the next one starts. ## Related - [Build a SaaS with an independent developer](https://erdibuilds.app/build/saas): Plan a SaaS product: accounts, subscriptions, technologies, an example milestone plan, what to write in the brief and how to pick a developer. - [Build a mobile app with a developer](https://erdibuilds.app/build/mobile-app): Plan an iPhone and Android app: typical technologies, an example milestone plan, what to put in the brief and how to spot a developer who fits. - [Build a web app with an independent developer](https://erdibuilds.app/build/web-app): How to plan a browser-based web app: common technologies, an example milestone plan, what to write in the brief and how to judge a developer. - [Hire a React Native and Expo developer](https://erdibuilds.app/hire/react-native-expo): One codebase for iPhone and Android: what React Native and Expo can do, what to ask a developer, example milestones and how matching works. - [Hire a Supabase developer for your backend](https://erdibuilds.app/hire/supabase): Supabase stores data and handles logins for apps. Learn what a Supabase developer does, what to ask, and how projects and matching work. - [How to Split a Project Into Milestones](https://erdibuilds.app/guides/how-to-split-a-project-into-milestones): Split a software project into milestones that each deliver something you can see and approve. Rules, an example plan and a free planner tool.