NightOwl Sleep Calc helps you choose bedtimes and wake-up times by counting full sleep cycles. A sleep cycle is the pattern your brain repeats through the night as you move through lighter sleep, deeper sleep, and REM. Many people average about a 90-minute cycle, which is why the calculator starts there—but everyone is different, so you can adjust the cycle length if you know you run shorter or longer.
The calculator also includes sleep latency, which is the time it typically takes you to fall asleep after you get into bed. If you usually drift off quickly, a lower latency may fit you better. If it often takes you longer—because of stress, caffeine, or screens—raise the latency setting so the recommendations match real life.
To use the tool, pick either "Wake up at…" to find the best time to go to bed, or "Bedtime now" to see when you might wake up feeling more refreshed. Each option shows a wake window: a flexible range (like 10 minutes) around the suggested time. That window makes planning easier, because you can aim for a range instead of a single exact minute while still staying close to an end-of-cycle wake-up.
Many adults feel best with about 5–6 cycles, which is roughly 7.5–9 hours of sleep time (plus sleep latency). If you're catching up on sleep, 6–7 cycles may feel better; if you're short on time, 4 cycles can be a workable minimum.
A full sleep cycle often averages around 90 minutes, but it can vary across people and across nights. That's why the cycle length setting is adjustable—use the default as a starting point, then tweak it if the results consistently feel early or late for you.
Sleep latency is how long it takes to fall asleep after you lie down. A common range is about 10–20 minutes, but it can be longer with stress, late caffeine, or bright screens. Set your latency to what's typical for you to keep the timing realistic.
Waking near the end of a cycle may reduce sleep inertia (the heavy, foggy feeling), since you're less likely to wake from deep sleep. Sleep isn't perfectly predictable, but cycle-based timing is a simple way to improve your odds.
A wake window is a small range around a recommended bedtime or wake time, like 10–15 minutes. It gives you flexibility without changing the overall cycle timing much, so you can choose what fits your routine while staying close to the plan.