On the math of attention spans

Suppose you have eight hours in a day for “work that matters.” Not meetings, not email, not the slow drip of Slack — the actual stuff. You sit down at 9:00.

It takes about 23 minutes to recover from an interruption, according to Mark et al., 2008. Call it $r = 23$ minutes.

If you are interrupted $n$ times during your block of $T = 480$ minutes, your usable time is approximately:

$$\text{usable}(n) = T - n \cdot r$$

Three interruptions and you’ve lost a fifth of your day. Seven interruptions and you have almost no focused time at all. The cliff is steep:

Interruptions	Usable focus
0	8h 0m
3	6h 51m
7	5h 19m
12	3h 24m
20	0h 20m

The takeaway is not “focus harder.” The takeaway is that the rate of interruption is the single biggest lever, and most of the levers that affect it are not internal at all — they are environmental, structural, and political.

If you find yourself unable to do deep work, do not start by blaming your willpower. Audit the room.