Anti-flicker cost calculator
Client-side A/B testing tools hide your page until their script has run. This works out what that wait costs in conversions and revenue. It all runs in your browser.
Example result
- Conversions lost a month
- 160
- Revenue lost a year
- $192,597
1,126 ms of hidden page takes the conversion rate from 3% to 2.68% on affected views, about $16,050 a month.
How it's worked out
Each 100 ms of hidden page keeps a fixed share of conversions, so the losses compound and can never pass 100%.
kept =(1 − loss per 100 ms)delay / 100
lost =visitors × affected × rate × (1 − kept)
With these inputs kept = (1 − 0.01)11.26 = 0.893, so 10.7% of affected conversions are lost: 50,000 × 100% × 3% × 10.7% = 160 a month.
- Extra delay
- How much later the page paints because of the snippet. In our open benchmark on a small Next.js page, a small stand-in testing script behind a standard anti-flicker snippet moved LCP from 757 ms to 1,883 ms (Lighthouse median of 9 runs), a gap of 1,126 ms. A real vendor script is larger, so treat that as a floor. The snippet's timeout is the worst case: Google Optimize and Webflow Optimize both shipped with 4,000 ms.
- Loss per 100 ms
- The default of 1% is an example input, not a finding. Deloitte's study for Google found retail mobile conversions 8.4% higher with a 0.1 s faster site, and Portent found B2B pages that load in 1 s convert 3 times better than pages that load in 5 s. Both are correlations across many sites, so use a figure you trust for yours.
- Affected page views
- Most snippets sit in the site-wide head, so every page view waits, including pages with no test running.
- What it leaves out
- Bounces before the page appears, the SEO effect of a slower LCP, and the flicker you get instead if you turn the snippet off.
Sources
- A/B testing on Next.js without flicker, the evolveAB benchmark (2026-11-11).
- Milliseconds make millions, Deloitte and Google case study on web.dev.
- Site speed is (still) impacting your conversion rate, Portent (2022).
- Anti-flicker prevention in Optimize, Webflow help (4,000 ms default).
- The anti-flicker tax, our longer write-up.
Hiding the page could be costing about $192,597 a year.
evolveAB picks the variant in your Next.js proxy before the page renders, so there's nothing to hide and no snippet in the head.
Planning a test? Size it with the sample size calculator.