Slow Website Impact Calculator
Calculate the impact of website speed on conversions.
Last updated: March 2026
A slow website revenue loss calculator shows how much money you lose from slow page load times. Every additional second of load time reduces conversions by approximately 7%. Google recommends pages load in under 2.5 seconds. Use this free tool to quantify your speed tax.
Monthly Revenue Lost
$70,000
Conversion Uplift Potential
14.0%% more conversions
Additional Monthly Conversions
140
Current Monthly Revenue
$500,000
How You Compare
Your average page load time is in the bottom 55% of all websites.
Industry typical: 2-5 seconds
Source: Google Core Web Vitals Report 2025
💡 What This Means
- 🔴 Your slow website is costing $70,000/month in lost revenue. Every second of delay above 2s reduces conversions by ~7%.
- 💡 Reducing load time to under 2 seconds could generate 140 additional conversions/month. Start with image optimization, CDN, and code minification.
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What is Page Speed Revenue Impact?
Page speed revenue impact quantifies the money lost due to slow website loading times. Research consistently shows that each additional second of load time reduces conversions by 7-12%. A site loading in 5 seconds converts roughly half as well as one loading in 2 seconds. Improve overall conversion with the Website Conversion Calculator and track funnel performance with the Conversion Rate Calculator.
The Formula
Revenue Lost per Month = Monthly Revenue × Conversion Drop per Extra Second × Additional Seconds of Load Time
Research shows each additional second of load time reduces conversions by 7-12%. A 5-second site converts roughly half as well as a 2-second site.
Worked Example
An ecommerce site generating £50,000/month revenue with a current 4.5-second load time vs a 2-second target. Estimated 8% conversion drop per second.
- Additional seconds = 4.5 − 2.0 = 2.5 seconds
- Conversion impact = 2.5 × 8% = 20% reduction
- Revenue lost = £50,000 × 20% = £10,000/month
- Annual impact = £10,000 × 12 = £120,000/year
📌 The slow site costs £10,000/month (£120,000/year) in lost revenue. A £5,000-15,000 speed optimisation project would pay for itself within 1-2 months.
Why This Matters
SEO ranking factor
Google uses Core Web Vitals (including Largest Contentful Paint) as a ranking signal. Slow sites rank lower, receiving less traffic, which compounds the conversion loss. Speed improvements boost both traffic and conversion rate simultaneously.
Mobile-first impact
Mobile connections are slower and less stable. A site that loads in 3 seconds on desktop may take 6-8 seconds on mobile. With 60%+ of traffic coming from mobile, slow mobile performance has an outsized revenue impact.
Common Mistakes
❌ Only testing on fast connections
Developers and marketers test on office Wi-Fi and see 2-second loads. Real users on 4G connections see 5-8 seconds. Always test on throttled connections (Chrome DevTools → Network → Slow 3G) to see what customers experience.
❌ Optimising the wrong metrics
Time to First Byte (TTFB) measures server speed, not user experience. Focus on Largest Contentful Paint (when main content is visible) and First Input Delay (when the page becomes interactive) — these are what users actually feel.
Industry Benchmarks
| Category | Good | Average | Poor |
|---|---|---|---|
| Load time | Below 2 seconds | 2-4 seconds | Above 5 seconds |
| Mobile speed score | 90+ | 50-90 | Below 50 |
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