B2C SaaS · Pre-Series-A
Next.js Performance Rescue Ahead of a Series A
Three-week audit + refactor of a Next.js App Router build that fell over at 100 concurrent users right before investor demos.
- Industry
- B2C SaaS · Pre-Series-A
- Duration
- 3 weeks
- Stack
- Next.js (App Router), React
Results at a glance
- LCP 4.8s → 1.2s
- INP 380ms → 120ms
- Held demo-day load without an infrastructure upgrade
Starting situation
A B2C SaaS start-up was preparing for its Series A. Its product was built with the Next.js App Router, and it fell over at 100 concurrent users, right before the investor demos were due.
Constraints
- A fixed deadline. The investor demos were scheduled, so the fix had to land within three weeks.
- The demo had to hold. The app needed to stay usable under demo-day load.
What was done
The work combined an audit and a refactor of the Next.js App Router build over three weeks. The audit located the bottlenecks, and the refactor removed them in the application itself.
If you want to see how this kind of work is approached, these articles describe the method:
- Next.js Performance Optimization in 2026: TTFB, Core Web Vitals, and the Profiling Workflow That Finds Real Bottlenecks
- React Website Performance: Fix LCP, CLS, and TTFB
Results
- LCP from 4.8s to 1.2s. Largest Contentful Paint measures when the main content of a page becomes visible. Google rates 2.5 seconds or less as good.
- INP from 380ms to 120ms. Interaction to Next Paint measures how quickly the page responds to clicks and key presses. Google rates 200 milliseconds or less as good.
- Demo-day load held without an infrastructure upgrade. The gains came from the application, not from more servers.
Stack and duration
Next.js with the App Router, on React. The engagement took three weeks.