Is a 20-minute nap enough before a night shift?

A brief nap can lift alertness for a couple of hours, NIOSH says. The pre-night naps it describes are longer, a few hours, to cut sleep pressure across the whole night.

Will a nap during the night shorten my day sleep?

Probably somewhat. The three-process model's authors estimated that a 2-hour nap during the night would shrink a 5-hour noon sleep to about 3.5 hours.

Does Capillary's alertness calculator include naps?

No. The shift alertness calculator assumes sleep from your schedule and leaves naps out, so it cannot show the benefit of a planned nap.

Napping before a night shift: when and how long

Updated October 8, 2026 · 2 min read

A long nap before a night shift improves alertness during the night. NIOSH's training for nurses calls it a prophylactic nap, usually a few hours long, and the studies it cites used naps of 1.5 to 3 hours ending between 17:00 and 22:00. Leave time for grogginess to clear before you start.

What the studies found

Naps before a night shift in studies cited by NIOSH
Nap	Clock time	Result
1.5 h	15:30 to 17:00	Nurses and nursing aides felt more alert in the second half of their first night shift
2.5 h	19:30 to 22:00	Better alertness during a simulated night shift than with no nap
3 h	14:00 to 17:00	Higher alertness during the night shift that followed

A 2006 study tested an evening nap before the first two of four night shifts. In the lab (68 people), the nap, caffeine and both together each improved alertness and performance, and the combination worked best. In the field (53 shift workers), the nap plus caffeine improved performance and lowered sleepiness.

NIOSH explains why a long nap works: it reaches the deeper stages of sleep, which can reduce the sleep pressure that builds through the night.

Timing the nap

Some hours are easier to sleep in than others. NIOSH lists the afternoon, around 14:00 to 16:00, as a time of extra sleep pressure, and late morning (11:00 to 12:00) and the 1 to 3 hours before your usual bedtime as hard times to fall asleep.

Example: your first night runs 23:00 to 07:00 and you got up at 07:00. Without a nap, by 05:00 you have been awake 22 hours, and the three-process model puts you below its sleepiness line from about 01:15. With a nap from 14:00 to 17:00, as in one study above, you start the shift 6 hours after waking instead of 16.

Grogginess after waking

Sleep inertia, the slowed, groggy state after waking, typically lasts 30 to 60 minutes, according to NIOSH. Deep sleep begins about an hour into sleep, and waking from it is worse. Waking after about 20 or about 90 minutes may leave less grogginess, which should clear within 15 to 30 minutes.

Naps during the shift

Where a department allows it, a short nap on shift also helps. In a randomized trial with 49 physicians and nurses on 12-hour nights in an academic emergency department, a 40-minute nap opportunity at 03:00 (about 25 minutes of sleep on average) led to fewer lapses on a vigilance test, less fatigue and less sleepiness at 07:30. Memory was briefly worse right after the nap, and the nap group drove no better on a simulated drive home.

The evidence is still thin. A 2016 Cochrane review rated trials of on-shift naps as low or very low quality and inconclusive, and a 2014 review found no study that measured workplace safety.

Common questions

Is a 20-minute nap enough before a night shift?: A brief nap can lift alertness for a couple of hours, NIOSH says. The pre-night naps it describes are longer, a few hours, to cut sleep pressure across the whole night.
Will a nap during the night shorten my day sleep?: Probably somewhat. The three-process model's authors estimated that a 2-hour nap during the night would shrink a 5-hour noon sleep to about 3.5 hours.
Does Capillary's alertness calculator include naps?: No. The shift alertness calculator assumes sleep from your schedule and leaves naps out, so it cannot show the benefit of a planned nap.

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