Your developer says the MVP is 90% done.
Here’s what that actually means in real numbers.
The first 90% is the part you can see. Screens load. Buttons work. The user can sign up, click around, and experience the core feature.
This is the part developers build fastest because it’s the most straightforward.
The last 10% is the part you can’t see. And it typically costs 2 to 3 times more than the first 90%.
Here’s what lives in that last 10%.
- Payment edge cases. What happens when a card is declined? When a subscription is canceled mid-billing cycle? When a user disputes a charge? Each one of these requires specific logic that doesn’t exist until someone builds it.
- Authentication edge cases. What happens when a token expires? When a user resets their password on one device while logged in on another? When someone tries to access an admin route without permission?
- Error handling. What does the user see when the server goes down? When they submit a form with invalid data? When their upload is too large? Right now, most of these scenarios show a blank screen or a cryptic error message.
- Deployment and monitoring. How does the code get from your developer’s laptop to the live server? Is it automated or manual? What alerts exist when something breaks at 2am?
- Security hardening. Input validation. Rate limiting. Data encryption. HTTPS enforcement. Headers that prevent common attacks.
This is why projects that are “90% done” take another 3 months.
The last 10% isn’t one thing. It’s fifty small things that each take real time to build correctly.
The solution isn’t to accept this as inevitable. The solution is to plan for it from the start.
Budget for the full 100%, not the visible 90%.
Has a developer ever told you a project was “90% done”? How long did the last 10% take?