Physics of Interaction · principle
Doherty Threshold
Playable Play this law (~3 min)or keep reading below ↓
Productivity soars when a system responds in under ~400ms, because neither the person nor the computer is left waiting on the other. Above that threshold attention drifts, the flow of work breaks, and the interface starts to feel sluggish — which is why fast perceived response time is one of the highest-leverage things you can design for.
See it on a real screen
Under ~400ms the app feels like an extension of you; past it, attention leaks away. Skeleton screens and optimistic taps (the heart fills before the server even answers) keep you under the line.
Where it comes from
In 1982, IBM researchers Walter J. Doherty and Arvind J. Thadani published 'The Economic Value of Rapid Response Time' in the IBM Systems Journal. Measuring real mainframe operators, they found that cutting computer response time below about 400 milliseconds didn't just save that fraction of a second — it changed how people worked, dramatically raising the number of transactions they completed per hour. It overturned the prevailing 2-second standard and put a number on a feeling every user knows: fast software makes you faster.
Origin: 1982 IBM mainframe terminal response-time studies
In the wild
- Optimistic UI
A 'like' turns red the instant you tap it — the app assumes success and reconciles with the server later, so you never wait.
- Skeleton screens
Facebook, YouTube and others show grey placeholder shapes while content loads, keeping perceived response under the threshold.
- Progress & motion
Purposeful animation and progress bars mask real latency; Nielsen's limits complement this — 0.1s feels instant, 1s keeps flow, 10s loses attention.
Further reading
Don't just read it — feel it.
Play the 3-minute game and let your own reactions prove the law.
Play the lesson