How to build a mobile app: a founder's guide from idea to the app stores
The decisions that matter before a line of code is written, and the ones you can safely put off.
Where do you start when building an app?
You start with one specific problem and the people who live with it. Before anyone opens Xcode or Android Studio, talk to potential users until their answers start repeating: what they do today, what it costs them, what they have already tried. Our guide on how to validate a startup idea covers the method in detail.
What you want from this stage is a single sentence: who opens the app, at what moment, to get what done. If you cannot write it, no framework will write it for you. If you can, you have the scope of your MVP: one core flow done properly, and a parking lot for everything else.
Should you build a web app, a cross-platform app or a native app?
It comes down to three questions: how much you need the phone's hardware, how much being in the app stores matters, and how many engineers will maintain the code. For most seed-stage startups the answer is one shared codebase that ships to iOS and Android. Fully native earns its cost when the product lives on hardware access, heavy graphics or real-time audio.
- Cross-platform app
- An app built from one codebase and shipped as a genuine store app on both iOS and Android, often on the web too. React Native, Flutter and Capacitor are three widely used routes; they differ in how they draw the interface and how much existing web code you can reuse.
| Approach | How it works | Best for | Trade-off |
|---|---|---|---|
| Web app or PWA | Runs in the browser and can be added to the home screen; iOS has supported web push for home-screen web apps since iOS 16.4 | Fast validation, B2B tools used on laptops as much as phones | No store listing, and some device features stay out of reach |
| Cross-platform (React Native, Flutter, Capacitor) | One codebase, two apps on the App Store and Google Play | Small teams that need both platforms from day one | Deeply native features go through plugins or platform-specific code |
| Native (Swift on iOS, Kotlin on Android) | Two separate apps, each in its platform's language | Hardware-heavy products, AR, real-time graphics or audio | Two codebases to maintain, with time and cost to match |
We compare the three frameworks properly in React Native vs Flutter vs Capacitor. If you are not yet sure you need a store app at all, read web app vs native app vs PWA first.
53.6%
The split tells you why platform-first debates rarely settle anything. A consumer app for the US market and a field-service tool for Southern Europe would make opposite bets. Look at the devices your first users carry rather than a national average; and if you go cross-platform, the question loses most of its weight anyway.
What are the steps to build a mobile app?
From problem to production
Problem and users
Interviews, observation, perhaps a test landing page. You leave with the one-sentence description and a handful of people willing to try a rough version.
Scope the first release
Write the core flow from launch to outcome. Everything that does not help complete it goes on the later list: social login, themes, advanced analytics.
Clickable prototype
Linked screens in Figma, put in front of real users. Changing a prototype takes hours; changing a shipped app takes weeks.
Architecture and backend
Accounts, data, payments, notifications, an admin panel. Decide early where personal data lives and how it is protected; our GDPR guide for startups covers the basics.
Build in short cycles
An installable build every week or two, with automated checks on every change, so progress is visible and course corrections are cheap.
Test on real devices
TestFlight on iOS (up to 10,000 external testers, with the first external build reviewed by Apple) and closed testing on Google Play, which is mandatory for new personal accounts.
Ship to the stores
Store listings, privacy disclosures, review. It is the step founders underestimate most, so we wrote a full guide on how to publish an app on the App Store and Google Play.
Measure and iterate
After launch two numbers matter more than downloads: how many people come back after the first week, and how many complete the core action. The roadmap starts there.
What do Apple and Google require before you can publish?
A developer account, a privacy policy and an app that follows their rules. The Apple Developer Program costs 99 US dollars per membership year (prices vary by region); enrolling a company requires a legal entity, a D-U-N-S Number and a public website on a domain the company owns. Google charges a one-off registration fee of 25 US dollars.
- If users can create an account, they must be able to delete it from inside the app (Apple guideline 5.1.1).
- The app must offer more than a repackaged website, as Apple's guideline 4.2 on minimum functionality puts it.
- New personal Google Play accounts must run a closed test with at least 12 testers opted in for 14 consecutive days before production access.
- Selling digital features or content inside the app generally means Apple in-app purchase and Google Play Billing, with regional exceptions you should check.
What did we learn building our own app?
Two habits we would recommend to anyone: continuous integration (ours runs on GitHub Actions) that checks every change before release, and nightly database backups with an off-site copy. Neither shows up in an investor demo, but both matter the day real users depend on you. The full story is in the Athleex case study.
Can you build an app without knowing how to code?
Yes, as far as a prototype or a first test with real users. No-code builders and AI coding assistants now produce working screens in days. The limits appear later: payments, permissions, personal data, performance and store review all need someone who can read and reason about the code.
The pattern we see working is to use these tools to learn fast, then decide deliberately what to rebuild. We cover it in how to build an MVP with AI and in no-code vs custom development.
Frequently asked questions
How much does it cost to build an app?
Scope drives the price more than anything: the number of flows, integrations, payments and platforms. On top come fixed costs such as Apple's 99 US dollars a year and Google's one-off 25 US dollars. We wrote a separate guide on what actually moves the number.
Should I launch on iOS or Android first?
It depends on where your users are: iOS leads in the US, Android leads across most of Europe. With a cross-platform codebase you can ship both for little extra effort. If you must pick one, look at the phones your earliest users carry.
Do I need a company to publish an app?
No, both stores accept individual accounts. With an organisation account, though, the company name appears as the seller, which is the cleaner option for a startup. Apple requires a legal entity, a D-U-N-S Number and a public website for organisations.
How long does app store approval take?
Apple says it typically reviews at least half of submissions within 24 hours and 90% within 48 hours. On Google Play, a new personal account must first complete a closed test of at least 14 days with 12 testers. Leave room in the plan for a rejection or two.
Can I build an app with AI?
You can build a working prototype and put it in front of real users. A production app still needs human review of security, personal data, payments and store rules. Use AI to go faster, not to skip those checks.
Sources
- Statcounter Global Stats, Mobile Operating System Market Share (Italia, Stati Uniti, settembre 2026) (19 October 2026)
- Apple, App Review Guidelines (19 October 2026)
- Apple, Apple Developer Program: enrollment (19 October 2026)
- Apple, TestFlight (19 October 2026)
- Google Play Console Help, App testing requirements for new personal developer accounts (19 October 2026)
- Google Play Console Help, Get started with Play Console (registration fee) (19 October 2026)
- WebKit, Web Push for Web Apps on iOS and iPadOS (16 febbraio 2023) (19 October 2026)
- Apple, App Review (tempi di revisione) (19 October 2026)
Figures and definitions checked on the dates shown.
