Nap Calculator

Why these two nap lengths?

A 20-minute nap is short enough that you stay in NREM Stage 2 (light sleep) the entire time. You don't descend into deep sleep, so you wake up without the adenosine-driven fog of sleep inertia. Studies — including a 2006 NASA study on pilot fatigue — show 20-minute naps improve alertness and reaction time within minutes of waking, with no recovery period needed.

A 90-minute nap is one complete sleep cycle: light sleep, deep sleep, and REM. You wake at the end, between cycles, so you don't experience sleep inertia either — but you get the restorative benefits of all four stages, including memory consolidation and physical recovery. Useful when you have time and a place to nap properly.

The 30–60 minute trap

Naps between 30 and 60 minutes are the worst option. You drop into NREM Stage 3 (deep sleep), your brain floods with sleep pressure, and you wake feeling worse than before you napped. The grogginess can last 30 minutes. If you find yourself waking up feeling terrible from a nap, you almost certainly fell asleep for too long.

Coffee nap — the only exception

If you have exactly 20 minutes and need maximum alertness, drink a cup of coffee immediately before lying down. Caffeine takes ~20 minutes to reach your bloodstream, so it kicks in just as you wake. Counterintuitive, but supported by research at Loughborough University — naps plus caffeine outperform either alone.

For full-night planning rather than naps, try the bedtime calculator or the 90-minute sleep cycle calculator.