How long is a sleep cycle exactly? ›

A sleep cycle lasts approximately 90 minutes, ranging from 80, 110 minutes depending on the individual, age, and how many cycles have already been completed that night. The first cycles of the night tend to be slightly shorter; later cycles, which contain more REM, can extend toward 110 minutes.

How many sleep cycles per night is normal? ›

Most adults complete 4, 6 complete sleep cycles per night. Five cycles (7.5 hours) is optimal for most adults according to the National Sleep Foundation. Fewer than 4 cycles consistently is associated with increased sleep debt and its downstream health effects.

What happens if you wake up in the middle of a sleep cycle? ›

Waking mid cycle, particularly during N3 deep sleep, triggers sleep inertia: a period of grogginess, slow thinking, and impaired reaction time that can last 20 to 90 minutes. Waking at the natural end of a cycle, when sleep naturally transitions to a lighter stage, eliminates most of this effect.

Is 7.5 hours of sleep better than 8 hours? ›

Often yes, when the timing matters. 7.5 hours aligned to complete 90 minute cycles typically produces less sleep inertia than 8 hours that cuts off 30 minutes into a new cycle. However, if 8 hours also happens to end at a cycle boundary (rare but possible), either duration can work well. Individual variation exists.

Do sleep cycles change as you get older? ›

Yes. Older adults tend to get less N3 deep sleep, which means their cycles are somewhat lighter on average. Teenagers get more N3 sleep and also experience a biological shift in circadian timing, which is why they naturally prefer later bedtimes. The 90 minute cycle architecture itself, however, remains consistent across ages.

Are 90 minute sleep cycles accurate for everyone?

Ninety minutes is an average. Research shows cycle length differs between people, and cycle length can vary within the same night. That is why bedtime calculators give estimates. They are still useful because they turn a vague goal into a realistic schedule you can test.

Is 8 hours too much sleep?

Eight hours sits inside the normal range. If you regularly need 10 or more hours and still feel unrefreshed, mention it to a doctor, because it can be linked with health conditions, medicines or poor quality sleep.

How do I adjust to daylight saving time?

Move your schedule by 15 to 20 minutes over several days before the change and get morning light afterwards. Expect a few days of adjustment.

Seasonal Bedding and Tog Selector: Right Duvet for Your Room

What the tog selector does

You enter your bedroom temperature, how warm you usually sleep, what you wear and whether you share the bed. The selector scores the situation and suggests a duvet tog, a fabric and a sleepwear tip.

It is a quick guide. Your own comfort always comes first, and you can adjust with a spare blanket.

What tog means

Tog is a UK unit of thermal resistance used on duvets. A low tog is light and cool, and a high tog is thick and warm. Shops usually sell 4.5 tog for summer, 7.5 to 10.5 for spring and autumn and 13.5 for winter. These bands are retail conventions. Many people use a 10.5 duvet all year or buy a combined set.

In the United States, duvets are described by fill weight and season. Use the same idea: light for warm rooms and heavy for cold rooms.

Why bedding matters for sleep

Okamoto Mizuno and Mizuno describe how a hot or cold sleeping environment changes sleep stages and body temperature, with heat usually raising wakefulness and reducing deep and REM sleep. Their later work with low air temperatures found that bedding and sleepwear help protect sleep in the cold.

The skin under the covers behaves like a small climate zone. Getting that right can matter as much as the room thermostat. Check the room with the bedroom temperature gauge.

Choosing fabrics

Cotton and linen breathe well in warm rooms
Bamboo and Tencel feel cool and wick moisture
Wool regulates temperature across seasons
Flannel and brushed cotton feel warm in winter
Synthetic fills can trap heat and moisture

Sleeping next to someone with different needs

Couples can use two single duvets on one bed, or one duvet with an extra blanket on the colder side. A fan on one side also helps. See sleep environment temperature.

If you sleep hot or sweat at night

Choose a lighter tog, breathable fabric and cooler sleepwear, and keep the room ventilated. Night sweats that soak the bed and come often need a medical check. See fix sleep with night sweats and why do I sweat at night.

Weighted blankets

Weighted blankets are popular for comfort but they add heat. Read weighted blanket sleep science for what research shows.

Babies and children

Babies need safe sleep clothing, not duvets or loose blankets. Follow the safe infant sleep guide. Children's needs differ, so check room temperature first.

Worked examples

A 14C bedroom in winter, with warm pyjamas and a person who runs cold, scores high and the selector suggests a 13.5 tog duvet with a wool or flannel layer. A 22C bedroom in early autumn with light sleepwear and a neutral sleeper lands on 7.5 tog.

In a 26C summer room with two people in the bed, the selector drops to 4.5 tog or a sheet only, since extra body heat adds to the load. If you are warm even then, use a fan and a cotton or linen sheet.

Caring for bedding so it keeps working

Wash covers weekly in warm water and duvets every few months according to the label. Damp or flat bedding insulates badly and can trigger allergies.

Air the bed in the morning by folding the duvet back for 20 minutes. If you suffer from dust mite allergy, choose washable synthetic fills and allergen proof covers, and speak to your doctor about treatment.

Frequently Asked Questions

What tog duvet should I use? ›

About 4.5 tog in summer, 7.5 to 10.5 in spring and autumn and 13.5 in winter, adjusted for your room and how warm you sleep.

What is a good bedroom temperature for sleep? ›

Roughly 15.6 to 19.4C (60 to 67F) for most adults.

Is a 10.5 tog good all year? ›

Many people use it year round with extra layers in winter.

What is the coolest fabric for bedding? ›

Linen, cotton percale and bamboo are popular for hot sleepers.

Does tog apply in the US? ›

Tog is a UK system. In the US look at fill weight and season labels.

Can babies use a duvet? ›

No. Use safe sleepwear and follow safe sleep guidance.

How this page was made

Written by F.A and last updated on 5 November 2026. Claims are checked against the peer reviewed papers and public health sources listed below, and findings from small or early studies are labelled as such. We follow our editorial policy and explain how times and results are calculated in our methodology. Calculators run in your browser and store nothing. Found an error? Tell us and we will correct it.

Sources

This page gives general information for adults and is not medical advice. If you have ongoing sleep problems, loud snoring, breathing pauses or heavy daytime sleepiness, speak to a doctor. Times and results are estimates.