Seven hours, every night, for ten years.

Where 7 hours sits

Below the consensus 8 by an hour. Above the chronic-restriction zone (≤6) where the body breaks even is impossible. Right on the edge.

For most adults, 7 hours is genuinely enough. The CDC, the AASM, the major sleep societies agree: 7 to 9 hours is the adult range. Seven is the floor of adequate.

For about a quarter of adults, however, 7 hours is a small chronic deficit. They need closer to 8. They feel fine on 7 because tolerance develops, but the body still under-repairs slightly, every night, indefinitely.

How to tell which group you are in

The face will, within five years, drift toward one of two trajectories:

• The 7-is-enough group: skin elasticity tracks normal aging curves. Eye structure ages with peer baseline. No visible signal of chronic deficit.
• The 7-is-just-under group: subtle drift earlier than peers. Eye structure ages 1 to 3 years faster than chronological. Skin recovery slows.

There is no easy upfront test for which group you are in. The most reliable signal is the face itself, observed across years.

What this means in practice

If you sleep 7 hours and feel great, you're probably in the first group. Continue. The mirror will confirm in a few years.

If you sleep 7 hours and feel mostly fine but suspect you'd be sharper on 8 — try 8 for a month. If the difference is real, you are in the second group, and the long-term face cost of 7 is worth the time investment.

Precog is one way to surface that difference. The portraits at year 5 are different between the two groups in ways the mirror can show.