Waking in the middle of a deep sleep stage is what makes you groggy. Enter your wake-up time and we'll find the bedtimes that let you rise at the end of a 90-minute cycle.
Your night isn't one long block of sleep — it's a series of 90-minute cycles, each moving through light sleep, deep sleep and REM (dreaming). Most adults need 5 to 6 cycles, or roughly 7.5–9 hours.
The trick to waking up refreshed isn't just sleeping longer — it's waking at the end of a cycle, when you're in light sleep, rather than being torn out of deep sleep. That mid-cycle jolt is called sleep inertia, and it's why you can feel worse after 8 hours than after 7.5.
You drift off and your body slows down. Easiest, gentlest stage to wake from.
Physical restoration and repair. Waking here causes the worst grogginess.
Dreaming, memory and mood processing. The cycle then restarts.
The average person needs about 15 minutes to drift off — we build this in.
The best bedtime is one that lets you wake at the end of a sleep cycle. Cycles run ~90 minutes, so aim for 5–6 full cycles (7.5–9 hours) plus ~15 minutes to fall asleep. Enter your wake time above and the calculator does the math.
About 90 minutes on average, cycling through light sleep, deep sleep and REM. Most adults need 5–6 cycles a night.
You're likely waking mid-cycle, in deep sleep. Waking at the end of a full cycle — say 7.5 hours instead of 8 — often leaves you more rested than the extra half hour would.
Around 15 minutes for the average adult. This calculator adds a 15-minute buffer so the times account for drifting off.