Why 90 minutes per sleep cycle?

A full sleep cycle — light sleep, deep sleep, then REM — averages about 90 minutes in adults. Waking at a cycle boundary, during light sleep, feels easier than being pulled out of deep sleep by an alarm mid-cycle.

How accurate is this calculator?

It's a planning aid, not a lab. Cycle length varies between people (70–120 minutes) and across the night. Treat the results as good starting points and shift by 15 minutes until your mornings feel right.

What is the 15-minute fall-asleep allowance?

Healthy adults take roughly 10–20 minutes to fall asleep. The calculator adds 15 minutes before the first cycle begins. If you know you drop off faster or slower, adjust the result accordingly.

Can I use this for naps?

Partly. A full cycle nap (~105 minutes including fall-asleep time) works with this math. For short naps, 20 minutes keeps you in light sleep and avoids grogginess — that's a different timer, not this one.

wake at the lightest point

Sleep Calculator

Q: How many cycles do I need?

Most adults do well on 5–6 cycles (7.5–9 hours). Four cycles is a workable floor for occasional short nights; three is a nap territory, not a night. Consistency beats duration — same wake time daily works better than chasing hours.

A full sleep cycle runs about 90 minutes. Count cycles from the moment you drift off, and the alarm lands in light sleep — waking that feels like surfacing, not being dragged. Or skip the math tonight — tired and horizontal beats optimal and upright.

it's now --:--

Assuming you drift off about 15 minutes from now.

wake up at 6 cycles is a full night for most adults

how to

Read the numbers like tides, not train times

step 1

Pick your direction

"If I sleep now" shows when each number of cycles would surface you. "I must wake at…" works backwards from the alarm to the moment you should be asleep.

step 2

Favour 5–6 cycles on a work night

That's 7.5–9 hours with the fall-asleep allowance. Four cycles works on short nights; three is a long nap with delusions. The highlighted card is where most mornings feel best.

step 3

Treat it as a starting point

Cycles vary person to person, and across the night. If mornings feel heavy, shift bedtime by 15 minutes and watch what happens for a week — your body will tell you what a train table can't.

why it works

Sleep is not a light switch

You don't descend into one long sleep — you cycle. Each round: light sleep, then deep, then REM, then back up. Roughly 90 minutes a lap. Near the top of each lap you're close to the surface; at the bottom of deep sleep you're nearly impossible to wake kindly.

An alarm at 7:00 after 6-and-a-half cycles rips you out of the deep — hence the heaviness that coffee only argues with. The same alarm after six whole cycles lands on the shallows: eyes open before the bell, or because of it. That's the whole trick — length to the boundary, not past it.

The calculator's one honest weakness: your cycles aren't exactly 90 minutes. Nobody's are. It's a compass, not GPS — still far better than waking at random.

The 15-minute allowance for falling asleep matters more than it looks: drift off 30 minutes late and every boundary slides. That's why the honest version of "sleep hygiene" is boring — same off-time, same alarm, and let the rhythm find its own depth.

questions

Five honest answers

Why 90 minutes per cycle?

A full cycle — light, deep, REM — averages about 90 minutes in adults. Waking at a cycle boundary, in light sleep, feels easier than being pulled out of deep sleep mid-cycle.

How accurate is this?

A planning aid, not a lab. Cycles vary between people (70–120 minutes) and across the night. Treat results as starting points and shift by 15 minutes until mornings feel right.

What's the 15-minute allowance?

Healthy adults take roughly 10–20 minutes to fall asleep. The calculator adds 15 before the first cycle. Know your own number? Adjust the result accordingly.

How many cycles do I need?

Most adults do well on 5–6 (7.5–9 hours). Four is a workable floor for short nights; three is nap territory. Consistency beats duration — same wake time daily works better than chasing hours.

Can I use it for naps?

Partly. A full-cycle nap (~105 minutes with fall-asleep time) fits this math. For short naps, 20 minutes stays in light sleep and avoids grogginess — a different timer, not this one.

keep resting Next stops on your map

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