What is the Doherty Threshold?
In 1982 Walter J. Doherty and Ahrvind J. Thadani of IBM published a paper on the economic value of fast response times. At the time, 2 seconds was considered an acceptable computer response. They showed that when response time dropped below about 400 ms, users worked dramatically faster — they stopped waiting and started flowing.
The Doherty Threshold and Core Web Vitals
| Metric | What it measures | Good value |
|---|---|---|
| Interaction to Next Paint (INP) | Delay between a user action and the next visual update | ≤ 200 ms |
| Largest Contentful Paint (LCP) | When the main content becomes visible | ≤ 2.5 s |
| Time to First Byte (TTFB) | How fast the server starts answering | ≤ 0.8 s (web.dev guidance) |
| Doherty Threshold | Response time that keeps users in flow | < 400 ms |
Core Web Vitals are Google's thresholds for real-user experience; the Doherty Threshold explains why they matter for behaviour, not just rankings.
How to make a site feel instant
Respond to every press immediately
Visible :active and :focus states confirm the action within milliseconds, even if the work continues.
Use optimistic UI
Show the expected result (a liked post, an added item) right away and reconcile with the server in the background.
Show progress for long tasks
Skeleton screens and progress bars make waits feel shorter and more predictable.
Speed up the server
Caching, a CDN and fewer database calls cut time to first byte.
Ship less JavaScript
Long tasks on the main thread are the main cause of slow interactions.
Lensux measures how long your server takes to start answering and compares it with the 400 ms Doherty Threshold. The full audit also measures layout shift and other render metrics in a real browser.
Frequently asked questions
Why 400 milliseconds?
It's the response time below which Doherty and Thadani observed users' productivity rising sharply in their IBM studies. It has since become a common target for perceived responsiveness.
Is the Doherty Threshold the same as INP?
No. INP is a specific Core Web Vitals metric for interaction latency with a 200 ms 'good' threshold. The Doherty Threshold is the broader behavioural principle behind such targets.