Free · 90-minute cycles · no signup
Sleep calculator
Wake up between cycles, not in the middle of one. Enter your wake-up time for cycle-aligned bedtimes, or see the best wake-up times if you go to bed now.
Ask about your actual schedule
The calculator does the cycle maths. Pro answers the messier question: how to move an existing sleep pattern, and what to change when the arithmetic alone is not the problem.
Example · “up at 5am Thursday, I usually sleep at midnight”
Three nights is enough to move a midnight bedtime to 9:45pm if you do it in steps rather than all at once. For a 5am wake, 9:45pm gives you five full cycles including time to fall asleep.
Move it 45 minutes a night
Midnight, then 11:15pm, then 10:30pm, then 9:45pm. Jumping straight to the target usually means lying awake for the two hours you gained.
Anchor the wake time first
Get up at 5am from the first morning even while the bedtime is still moving. The wake time drags the body clock; the bedtime follows it.
Bright light on waking
Ten minutes of daylight or a bright room within half an hour of getting up does more to shift the clock than anything you do at night.
Timing helps with a schedule you are choosing; if you are persistently tired regardless of when you sleep, that is worth raising with a doctor.
Why waking mid-cycle feels terrible
A night of sleep isn't uniform — it cycles through light sleep, deep slow-wave sleep, and REM roughly every 90 minutes. Waking from deep sleep produces sleep inertia: the groggy, heavy-headed state that can blunt alertness for a while after the alarm. Waking during light sleep at a cycle boundary is measurably gentler, which is the entire trick this calculator performs. The sleep-inertia research (Tassi & Muzet, and later Hilditch) is covered in our blog.
Pair it with the alarm
Once you have a target, set the alarm for it — the alarm card shows exactly how long you'll sleep. If mornings are the struggle, the 6:30 and 7:00 presets are one click.
Frequently asked questions
- How does the sleep calculator work?
- Sleep runs in cycles averaging about 90 minutes, moving through light sleep, deep sleep and REM. Waking at the end of a cycle tends to feel easier than waking mid-cycle. The calculator counts back from your wake time in 90-minute steps, plus about 15 minutes to fall asleep.
- How many sleep cycles do I need?
- Five to six cycles (7.5-9 hours) is the widely recommended range for adults — the calculator highlights those. Four cycles (6 hours) works occasionally; three is an emergency floor, not a plan.
- Are sleep cycles really exactly 90 minutes?
- No — they range roughly 80 to 110 minutes and lengthen through the night, which is why this is an estimate rather than a promise. If the suggested times consistently feel wrong, shift them 15 minutes and observe.
- What if I can't fall asleep in 15 minutes?
- Adjust mentally: if you know you take 30 minutes, aim to be in bed 15 minutes earlier than the suggested time. Consistency matters more than any single night.