How to build a SaaS from scratch: steps, timeline and cost

People who decide to build a SaaS usually show up with two questions: how much does it cost and how long does it take. Both have answers, but only after a third: what exactly goes into the first version. A SaaS is software customers access online and pay for every month. That brings demands a website or internal system doesn't have: billing on its own, keeping each customer's data separate, and holding up against outsiders trying to get where they shouldn't.

This guide walks through the steps in the order they happen, from the first test of the idea to the first paying customers. For each one, we show what weighs on timeline and cost, so you walk into a conversation with any vendor knowing what to ask.

Step 1: validate before you code

The first step has no code. It's confirming that people have the problem and are willing to pay to solve it.

The reason is concrete. In March 2026, CB Insights analyzed 431 venture-backed startups that shut down since 2023 and identified the cause in 385 of them. Poor product-market fit showed up in 43% of cases. Running out of money showed up in 70%, but CB Insights itself notes that's usually the final cause, not the root.

In practice, validating means:

• Talking to potential customers and hearing how they solve the problem today.
• Finding out how much they already spend on the current approach: spreadsheets, other software, people doing it by hand.
• Asking for a real commitment: a presale, a letter of intent, a paid pilot.

If nobody will pay even for a pilot, the SaaS isn't ready to be built. Finding that out takes weeks and protects the entire budget.

Step 2: discovery and scope cuts

Once the idea is validated, discovery comes next. This is where scope becomes a list: who uses it, what each role does, which integrations are mandatory and what waits for later.

The scope cut is the most important part. In April 2024, BCG recommended keeping the first version small for a tech project, something like three to four months of development, and only expanding once it proves its value. The same study suggests time-boxing the discovery phase and tying the project to a business outcome, not a list of screens.

Price and timeline come out of this step. Before it, any number is a guess.

Step 3: an MVP that bills, isolates and protects

A SaaS MVP isn't just the main screen. Three pieces need to be in it from the first paying customer.

Recurring billing

Without automatic billing, you become your own product's finance department. In Brazil, recurring billing has a new route: Pix Automático, which the Central Bank launched on June 16, 2025, according to Times Brasil | CNBC. Customers authorize once, set rules like a maximum amount, and later charges are debited on the due date. They can view and cancel the authorization in their bank app.

Recurring card payments and boleto still work. The point is to decide during discovery which methods are in, because each has its own rules for late payment, cancellation, plan changes and refunds.

Multi-tenancy

A SaaS serves many companies in the same system. In the industry, that's called multi-tenant. Each company should see only its own data, users and settings. Deciding on that separation early is cheap. Adding it later, with customers inside, is expensive and risky.

Access control

This is where most mistakes happen. In the 2025 edition of the OWASP Top 10, the list of web application security risks maintained by the OWASP Foundation, broken access control is still number one. And 100% of the applications tested had some form of it. In a SaaS, that means one customer seeing another's data. Login, permission roles and tests that try to break that separation belong in the MVP, not version 2.

Step 4: launch to a few, then to everyone

Launching isn't publishing and waiting. The order that reduces risk:

1. Open to a small group, ideally the people who took part in validation.
2. Measure: how many sign up, how many come back, where they get stuck, how many pay in month two.
3. Fix whatever blocks usage before investing in ads.
4. Open to the public.

Every problem found in the small group is a problem that never reaches a customer you paid to acquire.

Step 5: your first customers

First customers rarely come from ads. They come from the validation list, the founder's network and a website that explains the product in one sentence. Two things help a lot: a clear pricing page and a short path from sign-up to the first result inside the product. What happens in the first few minutes after sign-up matters as much as the ad that brought the person in.

What drives a SaaS timeline and cost

There's no list price for SaaS. What moves the number, as with any custom web system:

• The number of user roles and permission rules.
• Mandatory integrations: payments, invoicing, email, partner APIs.
• Billing methods and plan rules.
• AI inside the product, and what it can or can't do on its own.
• The volume of personal data and what the LGPD (Brazil's data protection law) requires for it.

That's why the serious path has three steps: discovery first, fixed price after, deadline written into the contract.

How we do it at the Studio

AI Vou Eu, an AI travel SaaS, went live in 4 weeks with the Studio. That deadline came out of discovery and was written into the contract. The price is also fixed after discovery, never before. The dev team is in-house, and we use Claude Code and Figma in design and build.

The code, files and access stay in the client's name. And every system ships with an AI agent that runs daily, flags failures, suggests improvements and checks that the data makes sense. In a SaaS with many companies inside, that agent is what raises the alarm early when something goes off track.

If you want to build a SaaS from scratch and need to know what goes into the first version, what it costs and when it goes live, the Studio's SaaS and custom system development service starts with that discovery.