How does the 90-minute sleep cycle work?

Sleep progresses through 4 stages (N1, N2, N3, REM) in cycles of ~90 minutes. Waking at the end of a cycle (rather than mid-cycle) reduces grogginess (sleep inertia).

What if I can't get 7.5 or 9 hours?

Aim for any complete cycle multiple: 4.5, 6, 7.5 or 9 hours. 6 hours of cycle-aligned sleep often feels more refreshing than 7 hours of mid-cycle interruption.

Does this account for falling-asleep time?

Yes — the calculator adds 14 minutes (average sleep-onset latency) before the first cycle begins. Adjust if you fall asleep faster or slower.

😴 Søvnberegner

Find the ideal bedtime or wake-up time based on 90-minute sleep cycles. Waking at the end of a cycle helps you feel refreshed rather than groggy. All calculations run in your browser — no data stored.

What would you like to calculate?

Wake-up Tid

Tid to Fall Asleep (sleep onset, minutes)

⚠️ Not medical advice. Søvnbehov varierer efter alder, helbred og individuel biologi. Denne lommeregner er en generel vejledning baseret på gennemsnitlig søvncykluslængde. Konsulter en søvnspecialist eller læge, hvis du oplever kronisk søvnløshed eller overdreven dagsøvnighed.

Om denne lommeregner

The Sleep Calculator is based on the science of sleep cycles. A typical adult sleep cycle lasts approximately 90 minutes and consists of four stages: light sleep (N1, N2), deep sleep (N3), and REM (Rapid Eye Movement) sleep.

Why Søvncykluss Matter

When you wake up mid-cycle — particularly during deep sleep (N3) — you experience sleep inertia: the feeling of grogginess, confusion, and reduced performance that can last 30–90 minutes. By timing your alarm to coincide with the end of a sleep cycle, you wake during lighter sleep and feel significantly more alert.

Hvor mange søvncyklusser har du brug for?

4 cycles (6 hours): Minimum for most adults — suitable only occasionally.
5 cycles (7.5 hours): Optimal for many adults. Recommended if you wake feeling tired at 6 hours.
6 cycles (9 hours): Ideal for teenagers, athletes, or those recovering from sleep debt.

Sleep Onset Latency

Den gennemsnitlige person tager 10–20 minutter at falde i søvn (søvnindtrædningslatens). Denne lommeregner tager højde for denne tid — hvis du falder i søvn med det samme eller tager længere end gennemsnittet, skal du justere feltet "tid til at falde i søvn" tilsvarende.

Recommended Sleep by Alder (NHS / WHO Guidelines)

Adults (18–64): 7–9 hours per night
Older adults (65+): 7–8 timer per nat
Teenagers (14–17): 8–10 timer per nat
School-age children (6–13): 9–11 hours per night

⚠️

Vigtig bemærkning: Dette værktøj er beregnet til at give estimater og bør ikke bruges som erstatning for professionel rådgivning. Oplysninger genereret af disse lommeregnere kan være ufuldstændige og tager ikke højde for alle individuelle omstændigheder. Søg altid rådgivning fra en certificeret ekspert (som en finansiel rådgiver, sundhedsperson eller licenseret ingeniør), inden du handler baseret på disse resultater.

Relaterede lommeregnere

TDEE Calculator — Totalt dagligt energiforbrug med BMR + skære/vedligeholde/bulk mål.
Water Intake Calculator — Daglige hydreringsbehov baseret på vægt, aktivitet og klima.
Daily Calorie Calculator — TDEE based on age, weight, height and activity level.