How Fast Is Fast Enough? [PerfNow 2025]

Tammy Everts

October 30, 2025

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1. How Fast Is Fast Enough? @tammyeverts #PerfNow

2. ¯\_(ツ)_/¯

3. Fast is magical. Catherine Jue, Co-founder at Kernel catherinejue.com/fast

4. Fast is magical. Fast eliminates cognitive friction. Raycast surfacing the

   right application before you finish typing feels like an extension of your mind. Superhuman's sub-100ms rule—plus their focus on keyboard shortcuts—changed the email game in a way that no one's been able to replicate, let alone beat. I recently used Mercury to pay another business that uses Mercury, and its instant settle felt surprising in a world where bank transfers usually take days. Catherine Jue, Co-founder at Kernel catherinejue.com/fast

5. Fast is magical. Fast eliminates cognitive friction. Raycast surfacing the

   right application before you finish typing feels like an extension of your mind. Superhuman's sub-100ms rule—plus their focus on keyboard shortcuts—changed the email game in a way that no one's been able to replicate, let alone beat. I recently used Mercury to pay another business that uses Mercury, and its instant settle felt surprising in a world where bank transfers usually take days. No one praises these tools explicitly for their speed. Catherine Jue, Co-founder at Kernel catherinejue.com/fast

6. Fast is magical. Fast eliminates cognitive friction. Raycast surfacing the

   right application before you finish typing feels like an extension of your mind. Superhuman's sub-100ms rule—plus their focus on keyboard shortcuts—changed the email game in a way that no one's been able to replicate, let alone beat. I recently used Mercury to pay another business that uses Mercury, and its instant settle felt surprising in a world where bank transfers usually take days. No one praises these tools explicitly for their speed. They just feel magical. Catherine Jue, Co-founder at Kernel catherinejue.com/fast

7. Fast is pragmatic.

8. Fast is pragmatic. You should make your site fast enough

   to improve business metrics like bounce rate and conversion rate.

9. Fast is pragmatic. You should make your site fast enough

   to improve business metrics like bounce rate and conversion rate. “If there’s no ROI, there’s no point in making pages faster.”

10. Pragmatic vs Magical

11. Pragmagical?

12. 12 @tammyeverts.com /tammyeverts

13. None

14. pragmatic magical

15. pragmatic magical

16. Who are you trying to please?

17. Who are you trying to please? Your boss?

18. Who are you trying to please? Your boss? Google?

19. Who are you trying to please? Your boss? Google? Your

    users?

20. Your boss*

21. Your boss* *the Very Important Person who sent you here

22. “We’re so cool, we don’t need to worry about site

    speed.”

23. Luckily, we can test that assumption!

24. None

25. 1. Slow site = fewer conversions

26. 1. Slow site = fewer conversions 2. Slow site =

    fewer return visits

27. 1.1 second Largest Contentful Paint (LCP) 6.2% conversion rate speedcurve.com/blog/site-speed-business-correlation/

28. speedcurve.com/blog/web-performance-plateau/

29. speedcurve.com/blog/site-speed-business-correlation/ 1.1 second is your GOAL 2.8 seconds is your

    THRESHOLD

30. 1. There’s no “one size fits all” correlation

31. 1. There’s no “one size fits all” correlation 2. If

    your metrics stay on the performance plateau, your business metrics don’t change

32. Google

33. speedcurve.com/web-performance-guide/get-started-with-core-web-vitals/

34. “We highly recommend site owners achieve good Core Web Vitals

    for success with Search and to ensure a great user experience generally. This, along with other page experience aspects, aligns with what our core ranking systems seek to reward.” developers.google.com/search/docs/appearance/core-web-vitals
35. None

36. Google thresholds ≠ Your business thresholds

37. contentsquare.com/blog/interaction-to-next-paint/

38. 200ms is “good” INP for Google

39. 200ms is “good” INP for Google speedcurve.com/blog/INP-user-experience-correlation/

40. speedcurve.com/blog/INP-user-experience-correlation/ 200ms is “good” INP for Google 50ms 150ms ???

    150ms
41. None

42. Your users

43. None

44. Metrics ≠ Feelings

45. People spending a long time on a web page or

    clicking on many links and visiting many pages can indicate that they're engaged… Kara Pernice President & CEO of Nielsen Norman Group

46. People spending a long time on a web page or

    clicking on many links and visiting many pages can indicate that they're engaged… Kara Pernice President & CEO of Nielsen Norman Group or totally lost.

47. People spending a long time on a web page or

    clicking on many links and visiting many pages can indicate that they're engaged… Kara Pernice President & CEO, Nielsen Norman Group A usability test might show us why the user is engaged or having trouble. or totally lost.

48. People spending a long time on a web page or

    clicking on many links and visiting many pages can indicate that they're engaged… Kara Pernice President & CEO of Nielsen Norman Group A usability test might show us why the user is engaged or having trouble. This is why I think of usability tests and site analytics as a perfect pairing for user research . or totally lost.

49. Engagement tasks vs Productivity tasks

50. Engagement tasks vs Productivity tasks Open ended, absorbing, potentially lengthy

51. Engagement tasks vs Productivity tasks Open ended, absorbing, potentially lengthy

    Higher tolerance for waiting

52. Engagement tasks vs Productivity tasks Open ended, absorbing, potentially lengthy

    Higher tolerance for waiting e.g., researching a trip
53. None

54. Engagement tasks vs Productivity tasks Fast completion of specific outputs

    Open ended, absorbing, potentially lengthy Higher tolerance for waiting e.g., researching a trip

55. Engagement tasks vs Productivity tasks Fast completion of specific outputs

    Lower tolerance for waiting Open ended, absorbing, potentially lengthy Higher tolerance for waiting e.g., researching a trip

56. Engagement tasks vs Productivity tasks Fast completion of specific outputs

    Lower tolerance for waiting e.g., administering your trip Open ended, absorbing, potentially lengthy Higher tolerance for waiting e.g., researching a trip
57. None

58. Same person, metrics, clicks, time on site…

59. Same person, metrics, clicks, time on site… Different user experience

60. One slow step can make the whole journey feel slow

    Sander van Surksum Founder of Iron/Out

61. Creating flow

62. “…a state in which people are so involved in an

    activity that nothing else seems to matter; Mihály Csíkszentmihályi Flow: The Psychology of Optimal Experience (1990)

63. “…a state in which people are so involved in an

    activity that nothing else seems to matter; the experience is so enjoyable that people will continue to do it even at great cost, for the sheer sake of doing it” Mihály Csíkszentmihályi Flow: The Psychology of Optimal Experience (1990)

64. Creating flow

65. Faking flow

66. 66 “We want you to be able to flick from

    one page to another as quickly as you can flick a page on a book. Urs Hölzle Google Fellow

67. 67 “We want you to be able to flick from

    one page to another as quickly as you can flick a page on a book. So, we’re really aiming very, very high here… at something like 100 milliseconds .” Urs Hölzle Google Fellow
68. None

69. pragmatic magical

70. pragmatic unique to your site magical 100ms

71. Pragmagical

72. Know who you’re trying to please

73. Know who you’re trying to please Know why users are

    on your site (engagement or productivity?)

74. Know who you’re trying to please Know why users are

    on your site (engagement or productivity?) Identify the right metrics and thresholds

75. Know who you’re trying to please Know why users are

    on your site (engagement or productivity?) Identify the right metrics and thresholds Meet your targets and mitigate regressions ASAP

76. Know who you’re trying to please Know why users are

    on your site (engagement or productivity?) Identify the right metrics and thresholds Meet your targets and mitigate regressions ASAP Never stop monitoring

77. Know who you’re trying to please Know why users are

    on your site (engagement or productivity?) Identify the right metrics and thresholds Meet your targets and mitigate regressions ASAP Never stop monitoring Do usability testing to avoid false assumptions

78. Know who you’re trying to please Know why users are

    on your site (engagement or productivity?) Identify the right metrics and thresholds Meet your targets and mitigate regressions ASAP Never stop monitoring Do usability testing to avoid false assumptions And most important…

79. 79 Always err on the side of creating an experience

    that isn’t just tolerable…

80. 80 Always err on the side of creating an experience

    that isn’t just tolerable… It’s delightful.

81. Thank you! :) @tammyeverts.com /tammyeverts