Software as a service means customers pay to use software that you run for them. That changes the cost model compared with building a one-off tool for one client.
What is on top of a normal web app
- Accounts and organisations. Many customers, each with several users, kept strictly apart.
- Subscriptions and billing. Plans, trials, upgrades, failed payments, invoices, taxes.
- Onboarding and settings. Customers need to get started without calling you.
- Admin tools. For you to look up accounts, help people and see what is happening.
- Operations. Monitoring, backups, updates and incident response, indefinitely.
- Compliance and trust. Data protection, security posture, terms of service.
Where founders underestimate
Usually not the first version, but everything after: support, fixing edge cases found by real customers, and continued development while paying for hosting and tools. A rule of thumb that holds up is to plan a budget for at least a year of running and improving, not only the launch.
How to stay in control
- Launch with one plan and a small feature set.
- Use established services for payments, email and sign-in.
- Keep the architecture simple until real load demands more.
- Track the cost of serving one customer, so growth does not surprise you.
I do not quote a figure, because it depends on scope more than anything else. A written list of the first version’s features and the integrations needed is enough to get a useful range.