Free · no signup · shows its working
Sleep calculator that shows its working
Enter your wake time and this sleep calculator returns the bedtimes that land you at the end of a sleep cycle — 5 cycles of 90 minutes plus 15 minutes to fall asleep means in bed by 10:45 pm to wake at 6:30 am. Unlike most sleep calculators, the cycle length and the time-to-fall-asleep are adjustable, because 90 minutes is an average, not your personal constant.
90 min is the average — yours may differ.
10–20 min is typical for a healthy sleeper.
Go to bed at one of these times
the arithmetic · 5 cycles × 90 min + 15 m to fall asleep = 7 h 45 m in bed → in bed by 10:45 pm to wake at 6:30 am
Waking at the end of a cycle — rather than mid-cycle in deep sleep — is what makes an alarm feel bearable. The highlighted option gives most adults enough total sleep; pick a longer one if you're repaying debt.
Planning tool, not medical advice. These figures are population averages for scheduling your sleep — they don't diagnose or treat any condition. See a clinician for persistent sleep problems.
The whole sleep-planning toolkit
One shared model — your sleep need, your chronotype, your wake time — drives every tool below. Start with the chronotype quiz if you've never thought about your timing.
Bedtime Calculator
Enter your wake time — get the bedtimes that land you at the end of a sleep cycle.
Calculate Wake Up Time
Going to bed at a set time — get the alarms that land you at a cycle boundary.
Sleep Cycle Calculator
90 minutes is only an average — count your cycles with a configurable cycle length.
90 Minute Sleep Cycle Calculator
The 90-minute rule applied properly — with the falling-asleep time most tools skip.
Chronotype Quiz
Lion, bear, wolf or dolphin — 16 questions, transparent scoring, no email gate.
Chronotype Test
The same 16-question test with the scoring ledger shown answer-by-answer.
How Much Sleep Do I Need
Age-banded sleep need from the National Sleep Foundation's published ranges.
Sleep Debt Calculator
Log your last two weeks — see the debt, and a realistic plan to repay it.
Wind-Down Routine Planner
A personalised pre-bed schedule, worked backwards from your bedtime. Printable.
Sleep Schedule Calculator
A full week of bedtimes and alarms — including shift-work anchor schedules.
Nap Calculator
Power nap, slow-wave or full cycle — the right nap length and its best window.
REM Sleep Calculator
How much REM a night actually contains, and why your last cycles hold most of it.
Sleep Age Calculator
A playful composite of how your sleep habits compare to your age. Honest about what it is.
Sleep Efficiency Calculator
Time asleep ÷ time in bed — the metric sleep clinics actually track.
Circadian Rhythm Calculator
Light-timing anchors that keep your body clock set: when to seek it, when to dim it.
Jet Lag Calculator
Direction-aware recovery: how long adjustment takes, and how to pre-shift before you fly.
Methodology & sources
Every figure on this site, cited. The model, the maths, the references.
Why most sleep calculators get it wrong
They hardcode two numbers that are only averages: a 90-minute cycle and zero time to fall asleep. Real cycle length runs 70–120 minutes between people, and a healthy sleeper takes 10–20 minutes to drop off. Ignore the latency and every recommended bedtime is quietly 15 minutes too late — you spend the first cycle half-awake. Every tool here exposes both assumptions as inputs, shows the arithmetic with your own numbers substituted in, and keeps the result above the fold with no signup wall between you and the answer.
Sleep calculator FAQ
How does this sleep calculator work?
It counts sleep in cycles of about 90 minutes — the average length of one trip through light sleep, deep sleep and REM. You give it a wake time; it subtracts whole cycles plus the time you take to fall asleep (default 15 minutes) and returns the bedtimes that land you waking at the end of a cycle rather than in the middle of deep sleep. Both the cycle length and the latency are adjustable, because 90 minutes is a population average, not a rule.
What time should I go to bed to wake up at 6:30 am?
With an average 90-minute cycle and 15 minutes to fall asleep: 10:45 pm for 5 cycles (7 h 30 m of sleep), 9:15 pm for 6 cycles (9 h), or 12:15 am for 4 cycles (6 h). Most adults should take the 5-cycle option. Enter your own wake time above to get exact figures for your cycle length.
Is the 90-minute sleep cycle real?
It is a real average, not a constant. Published cycle lengths range roughly 70–120 minutes between people, and your own cycles lengthen across the night — early cycles are deep-sleep heavy, late cycles REM-heavy. That is why every calculator on this site lets you change the cycle length instead of hardcoding 90.
Is this free? Do I need an account?
Everything on this site is free with no account, no email and no signup. Your inputs are stored only in your own browser (localStorage) so settings persist between visits; nothing is uploaded.
Is this medical advice?
No. These are planning tools built on population averages for scheduling sleep. They do not diagnose or treat insomnia, sleep apnoea or any other condition. If poor sleep persists for more than a few weeks, see a clinician.