# Why site performance matters

**Author:** Vercel

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Site performance directly affects revenue. A one-second delay in page load time can reduce conversions measurably, making performance one of the highest-ROI investments for any web team. This guide covers the key factors that affect performance, how Google measures them, and how improvements translate to business outcomes.

## Key performance factors

Seven elements have the most impact on site performance:

1. **Page load time** measures the speed of full webpage rendering
   
2. **Server response time** measures how quickly the server responds to browser requests
   
3. **Resource optimization** covers efficient management of images, scripts, and stylesheets
   
4. **Caching** stores frequently accessed resources closer to the user
   
5. **User experience (UX)** reflects overall interaction quality and accessibility
   
6. **Code efficiency** determines how well frontend code (HTML, CSS, JavaScript) performs
   
7. **Content delivery networks (CDN)** use geographically distributed servers to reduce latency
   

## Impact on user experience and brand perception

Performance directly shapes buying behavior:

- 45% of consumers say they're less likely to make a purchase when the site loads slower than expected
  
- Users are 26% more willing to recommend an ecommerce site if load times reduce from 10 seconds to 3 seconds
  
- 61% of customers have stopped buying from a company because a competitor provided a better experience
  

Dynamic personalization historically conflicted with performance. Middleware solutions now enable prebuilt page variants, delivering both speed and personalization.

## Core Web Vitals and SEO

Google uses three Core Web Vitals metrics as ranking signals:

### Largest Contentful Paint (LCP)

LCP measures loading performance, specifically the time for the largest content element to become visible. The target is 2.5 seconds or less.

### Interaction to Next Paint (INP)

INP measures responsiveness, or how quickly the page reacts to user input after content loads. The target is under 200 milliseconds.

### Cumulative Layout Shift (CLS)

CLS measures visual stability by tracking unexpected element movement during loading. The target is a CLS score below 0.1.

## Revenue impact

Strong Core Web Vitals performance drives revenue through three mechanisms:

**Increased organic traffic.** Higher search rankings generate more clicks from results pages.

**Higher conversion rates.** Optimized Core Web Vitals improve the user experience, which converts more visitors to customers.

**Competitive advantage.** Superior search visibility and user experience attract customers away from competitors.

**Case studies**

- Rakuten achieved a 53.4% increase in revenue per visitor and a 33.1% increase in conversion rate after improving Core Web Vitals
  
- Yelp reduced First Contentful Paint by 45% and observed a 15% improvement in their conversion rate
  

## Conclusion

Performance, personalization, and SEO work together. Engineering investments in site performance translate directly to measurable business outcomes through improved user retention, conversion rates, and revenue growth.

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