Page Speed Impact Calculator
The Cost of a Slow Page
Load time doesn't just affect crawl budget and Core Web Vitals scores — it changes visitor behavior in a measurable way. Widely-cited industry analyses have repeatedly found that conversion rates fall as load time climbs past a fast baseline. This calculator applies that relationship to your own numbers so a page speed regression can be expressed in the metric that matters to the business: estimated lost conversions.
The Formula
Conversion Drop % = max(0, Extra Load Time) × 7%
Estimated New Conversion Rate = Current Conversion Rate × (1 − Conversion Drop % ÷ 100)
The 7%-per-second figure is a widely-cited industry rule of thumb for the relative conversion impact of added load time, not a precise prediction for any individual site — actual sensitivity varies by traffic source, device mix, and how far into the load the key content appears.
Where This Matters
- Justifying a performance budget — translating "the homepage got 1.5 seconds slower" into an estimated conversion impact makes the case for engineering time.
- Post-deploy regression checks — catching the conversion cost of a recent slowdown before it shows up in revenue reports.
- Prioritizing which pages to optimize — running the calculation against your slowest, highest-traffic pages first.
Estimated Conversion Drop by Extra Load Time
| Extra Load Time | Estimated Conversion Drop |
|---|---|
| 0.5s | 3.5% |
| 1.0s | 7.0% |
| 2.0s | 14.0% |
| 3.0s | 21.0% |
| 5.0s | 35.0% |
| 10.0s | 70.0% |
Drop is capped at 100% and based on a general industry rule of thumb, not a site-specific measurement.
How to Use This Calculator
- Enter your page's current load time in seconds.
- Enter a baseline or target load time in seconds (defaults to 1 if left blank).
- Optionally enter your current conversion rate to also see an estimated new rate.
- Select Calculate to see the estimated conversion drop.
Related Calculations
Once you've quantified traffic value, see how it compounds with the Organic Traffic Value Calculator, or check click-through expectations with the SERP CTR Calculator.