A web app that loads in one second converts signups at roughly 39%. At six seconds, that drops to about 18% — less than half. This isn't a rough industry rule of thumb; it's the finding of Portent's large-scale study across 27,000+ landing pages and 5.6 million sessions, one of the most-cited page-speed datasets in use today. The relationship holds across load-time bands, not just at the extremes, which is what makes it useful for prioritizing engineering work rather than just a talking point for a pitch deck.
The Core Numbers, Sourced
| Load time | Average conversion rate |
|---|---|
| 1 second | ~39% |
| 2 seconds | ~34% |
| 3 seconds | ~29% |
| 6 seconds | ~18% |
Portent's separate 2022 analysis of 27,000+ landing pages and 5.6 million sessions found ecommerce pages loading under 2 seconds converted at 3.05%, compared to 1.94% for pages loading in 3–4 seconds — a 57% relative drop from a 2-second difference. The pattern isn't unique to ecommerce. Mobile-specific research shows a 1-second delay in mobile load time can reduce conversions by up to 20%, and 53% of mobile visits are abandoned outright if a page takes longer than 3 seconds to load, according to Google's own "Think with Google" research.
Why This Matters More for Signup Flows Than for Content
Signup and onboarding flows are unusually speed-sensitive compared to general content pages, for a structural reason: a visitor evaluating a web app is almost always comparing it to at least one competitor in the same tab-switching session. A content page has to hold attention; a signup page has to win a comparison that's actively happening in real time. A prospect who hits a slow-loading signup form doesn't necessarily conclude your product is bad — they just move to the tab that's already loaded. That's a harder kind of loss to recover from through remarketing, because it happened before they ever evaluated the actual product.
The Milestone-Level Data: Small Improvements Compound
The relationship isn't limited to large jumps between whole seconds. Case-study-level data collected by WPO Stats across 200+ companies shows conversions increasing between 2% and 7% for every one-second improvement, depending on sector and starting point — and separate research shows a 0.1-second speed improvement alone can lift conversions by 8.4% in retail and 10.1% in travel. For a web app with meaningful signup volume, that means performance work doesn't need to hit a dramatic before/after milestone to matter; incremental gains compound because the relationship holds across the whole curve, not just at round numbers.
Core Web Vitals: What They Measure and Why They're Not Optional
Google's Core Web Vitals give a standardized way to measure the experience behind these conversion numbers: Largest Contentful Paint (LCP) under 2.5 seconds, Interaction to Next Paint (INP) under 200 milliseconds, and Cumulative Layout Shift (CLS) under 0.1. Only 42–51% of mobile sites currently pass all three thresholds, according to recent aggregated data — meaning roughly half of the web is shipping an experience Google itself classifies as underperforming, on the exact metrics tied to the conversion numbers above.
An Honest Caveat: Correlation, and a Genuinely Weak Link to AI Search
It's worth being precise about what the data does and doesn't show. Faster sites often also have better design, clearer messaging, and fewer technical problems generally — speed and conversion moving together doesn't prove speed is the only cause, even though the documented A/B test cases (single-variable tests where speed was the only thing changed) support a real causal effect, not just correlation. Separately, and worth knowing if speed work is being justified partly on AI-search grounds: a January 2026 Search Engine Land analysis of 107,000+ pages found Core Web Vitals have only a weak direct correlation with getting cited in Google AI Overviews, with an LCP correlation as low as -0.12. Page speed is a real, well-documented conversion lever. It is not, on its own, a reliable AI-citation lever — the two arguments for investing in it are separate, and only one has strong supporting data.
What to Prioritize First
- Measure your actual signup-page LCP with PageSpeed Insights or an equivalent tool before optimizing anything — you can't prioritize what you haven't measured. Slow server response time is a common, often-overlooked culprit worth ruling out via your hosting before touching front-end code.
- Treat the signup/onboarding flow as higher-priority than general content pages, given the comparison-shopping dynamic specific to that flow.
- Don't wait for a dramatic full-second improvement to ship a fix. The data shows gains compound from tenths of a second, not just whole-second milestones.
- Check mobile specifically, since mobile delay has an outsized effect (up to 20% conversion loss per second) and mobile Core Web Vitals pass rates remain well under desktop.
- Justify speed investment on conversion data, not AI-citation hopes. The conversion case is strong and well-documented; the AI-search case for speed specifically is currently weak.
The relationship between load time and signup conversion is one of the more consistently replicated findings in web performance research — not because any single number is precise to the decimal, but because the direction and rough magnitude show up across genuinely independent datasets, from Portent's large-scale study to Google's own mobile research to hundreds of individual company A/B tests.