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Sleep Calculator

What time should you go to bed, and when should you wake up? Using the 90-minute sleep cycle method, find your ideal bedtime and wake-up time, your power nap length, and your sleep debt — instantly, with a clear explanation.

1 cycle ~90 min Ideal 5–6 cycles Recommended 7.5–9 hrs Updated: Jul 19, 2026
We'll highlight the row(s) that best match your age group's recommended sleep range.
Enter your wake-up time and we'll suggest the ideal bedtimes that land on the end of a sleep cycle.
Enter your bedtime and we'll show the wake-up times that leave you most refreshed.
🌙 If you lie down right now, we'll use your device's clock to show the wake-up times that land on the end of a sleep cycle. Nothing else to enter — just tap Calculate.
Enter the time you went to bed and the time you woke up, and we'll show how many hours, how many cycles, and the overall sleep quality:
⚙️ Advanced — time to fall asleep
How many minutes does it typically take you to fall asleep after getting into bed? This is factored into the calculation.
Quick answer To find your ideal bedtime, count back 90-minute sleep cycles from your desired wake-up time. For example, to wake at 7:00 AM, aim for 9:45 PM (6 cycles) or 11:15 PM (5 cycles), including about 15 minutes to fall asleep. Waking at the end of a cycle — not in the middle of deep sleep — is what makes you feel most refreshed.
90 min1 sleep cycle
5–6Ideal cycle count
7.5–9 hrsRecommended sleep
10–20 minIdeal power nap
⚠️ Health note: This tool is for informational purposes only and is not a substitute for medical advice. The 90-minute cycle is an average and can vary from person to person (80–120 minutes). If you experience ongoing insomnia, snoring, sleep apnea, or excessive daytime sleepiness, please see a doctor or sleep specialist.
😴 Sleep Calculator — ToolPico ↗

What is a sleep calculator, and how does it work?

A complete guide — with the 90-minute sleep cycle method — to finding your ideal bedtime and wake-up time, and why waking at the end of a cycle matters.

A sleep calculator uses the fact that sleep progresses in 90-minute cycles to find the bedtime and wake-up times that will leave you feeling most refreshed. Sleep isn't one uniform block through the night — cycles of light sleep, deep sleep, and REM (dreaming) sleep follow one another. Waking during the lightest part of a cycle leaves you feeling energized; waking in the middle of deep sleep causes sleep inertia, a temporary grogginess. The calculator above handles four common questions — bedtime, wake-up time, "if I sleep now," and total sleep duration — instantly and with an explanation.

What time should I go to bed?

Quick answerCount back 5 or 6 full cycles (7.5–9 hours) from your target wake-up time, then add about 15 minutes for the time it takes to fall asleep. Just enter your wake-up time in the "What time should I sleep?" tab above — the calculator lists every cycle-end bedtime, color-coded green, amber, or red.

What is a 90-minute sleep cycle?

Quick answerA full sleep cycle — moving from light sleep into deep sleep and then REM — averages 90 minutes in adults. You complete 4–6 cycles per night, and a good night's sleep is usually 5–6 cycles. Cycle length varies from person to person (80–120 minutes), so recommended times are estimates.

How many hours of sleep do I need?

Quick answerAdults are generally advised to get 7–9 hours a night, about 5–6 cycles. Adults 65+ need roughly 7–8 hours, teenagers 8–10 hours, and school-age children 9–11 hours. Consistently sleeping under 6 hours is considered insufficient long-term. See the detailed age table in the "Reference" section below.

How long should a power nap be?

Quick answerThe most effective power nap is 10–20 minutes — short enough that you don't enter deep sleep, so you wake up more alert without grogginess. A 30–60 minute nap can involve some deep sleep, causing brief grogginess on waking. A full 90-minute nap completes an entire cycle (including REM) with the least grogginess. Napping in the early afternoon avoids disrupting nighttime sleep.

How is a sleep cycle calculated?

Quick answerYou choose an anchor time — when you want to wake up, or when you'll go to bed. From that time, 90-minute blocks are counted backward or forward, with roughly 15 minutes added for the time it takes to fall asleep. Times landing on 4, 5, and 6 cycles are shown, with 5–6 cycles (7.5–9 hours) as the ideal range. This calculator automates the whole calculation and flags times that fall mid-cycle.

What time should I go to bed? (examples by wake-up time)

Assumes 15 minutes to fall asleep. 5 cycles = 7.5 hours, 6 cycles = 9 hours of sleep — both are in the ideal range.

Recommended bedtimes by wake-up time (includes 15-min sleep latency)
Wake-up time6 cycles (9 hrs)5 cycles (7.5 hrs)
6:00 AM8:45 PM10:15 PM
6:30 AM9:15 PM10:45 PM
7:00 AM9:45 PM11:15 PM
7:30 AM10:15 PM11:45 PM
8:00 AM10:45 PM12:15 AM

Popular calculations

Power nap & sleep debt

Two quick tools: get the most out of a short nap, and see how much sleep debt has built up over the week.

âš¡Power nap calculator
If you lie down now, this shows when to get up for the nap length you choose (assumes 5 minutes to fall asleep).
📊Sleep debt calculator
Shows the weekly gap between the sleep you're actually getting and your target.
📅 Log a full week instead (7-day sleep log)
Enter the hours you actually slept each night. Leave a day blank to skip it.

What's your chronotype? (30-second quiz)

Your chronotype is your body's natural tendency toward morning or evening activity. Answer 5 quick questions to find out whether you're a Lion, Bear, Wolf, or Dolphin — and get one tip to work with it instead of against it.

Question 1 of 5

Reference tables & practical facts

Citable figures: recommended sleep by age, cycle-to-duration conversions, and nap types. These are evergreen, generally accepted values that don't change year to year.

Recommended daily sleep by age group
Age groupRecommended
Newborn (0–3 months)14–17 hours
Infant (4–11 months)12–15 hours
Toddler (1–2 years)11–14 hours
Preschooler (3–5 years)10–13 hours
School-age child (6–13 years)9–11 hours
Teenager (14–17 years)8–10 hours
Young adult (18–25 years)7–9 hours
Adult (26–64 years)7–9 hours
Older adult (65+ years)7–8 hours

Source: National Sleep Foundation general recommendations. Individual needs may vary.

Number of sleep cycles → total sleep duration
CyclesSleep durationAssessment
3 cycles4.5 hoursInsufficient
4 cycles6 hoursShort
5 cycles7.5 hoursIdeal
6 cycles9 hoursIdeal (upper end)

One cycle is assumed to be ≈ 90 minutes. Total time in bed is found by adding time to fall asleep (~15 min) to this figure.

Nap types and their effects
DurationWhat it's good forGrogginess
10–20 minQuick refresh, focus & alertnessNone
30 minModerate restPossible, brief
60 minMemory & cognitive performancePossible
90 minFull cycle, REM, creativityLeast

The ideal time for a nap is early afternoon (roughly 1:00–3:00 PM). Long naps late in the day can make it harder to fall asleep at night.

Add this calculator to your site (embed code)

Embed the sleep calculator on your own website for free. Copy the code below into your HTML — the tool runs in a simplified view and links back to this page as its source.

The embedded tool has a fixed layout; you can adjust the height value to fit your site. No ads or personal data, runs entirely client-side.

Sleep terms glossary

Short definitions of the core terms used in sleep calculations.

Sleep cycleA complete round of sleep including light sleep, deep sleep, and REM, averaging about 90 minutes in adults.
REM sleepThe stage where dreaming occurs and eye movement speeds up. Important for memory and learning; it lengthens toward the end of each cycle.
Deep sleepThe stage where the body rests most and waking is hardest. Waking in the middle of it causes grogginess.
Sleep inertiaThe temporary grogginess and difficulty concentrating felt after waking from deep sleep.
Sleep latencyThe time it takes to actually fall asleep after getting into bed; averages about 15 minutes.
Power napA short 10–20 minute nap that boosts alertness and focus without entering deep sleep.
Sleep debtThe accumulated gap between the sleep you need and the sleep you actually get.
Circadian rhythmThe body's roughly 24-hour internal clock that governs the sleep-wake cycle and responds to light.
ChronotypeYour natural tendency toward morning or evening activity, commonly grouped as Lion, Bear, Wolf, or Dolphin.

In-depth guides

Detailed answers to the most common sleep questions.

Why do I wake up tired even after 8 hours of sleep?

Total sleep time isn't the only thing that matters — where your wake-up time falls within a cycle matters too. Even after 8 hours, if your alarm catches you in the middle of deep sleep, you'll experience sleep inertia and wake up tired. The 90-minute cycle method is designed to solve exactly this: it times your wake-up for the lightest part of a cycle.

Try entering your target wake-up time above and going to bed at one of the recommended (green) times. Caffeine, alcohol, late-night screen light, and irregular bedtimes can also lower sleep quality, leading to the "I slept enough but don't feel rested" feeling.

How to build a sleep schedule for students and shift workers

If your time is limited, prioritize completing full cycles: sleeping 6 hours (4 cycles) instead of 5 can leave you more refreshed than 5 hours split mid-cycle. Use the "My sleep duration" tab to see how many cycles your current bedtime and wake-up time add up to.

To make up a daytime deficit, a 20-minute power nap is the safest option; a full 90-minute nap gives deeper recovery. If you work shifts, darkening your sleep environment and keeping a consistent sleep window — even if it's not at night — helps protect your circadian rhythm.

How to become an early riser

The key to waking early and feeling refreshed is consistency. Going to bed and waking up at the same time every day — weekends included — anchors your circadian rhythm. Count back 5–6 cycles from your target wake-up time and start going to bed at that time; your body will adjust within a few days.

Getting morning daylight right away (opening curtains, stepping outside) shifts your internal clock earlier and makes you naturally sleepier earlier in the evening. Cutting bright screens and caffeine in the evening also helps. Setting an alarm for the bedtime this calculator recommends can speed up the transition.

Frequently asked questions

What time should I go to bed?
To find your bedtime, count back 90-minute sleep cycles from the time you want to wake up, then add about 15 minutes to fall asleep. For example, to wake at 7:00 AM, go to bed at 9:45 PM for 6 cycles (9 hours) or 11:15 PM for 5 cycles (7.5 hours). Waking at the end of a cycle gives you the most refreshed start.
What is a 90-minute sleep cycle?
Sleep moves through cycles of light sleep, deep sleep, and REM, and a full cycle averages about 90 minutes in adults. A typical night includes 4–6 cycles. Waking during the lightest part of a cycle leaves you feeling refreshed; waking in the middle of deep sleep causes sleep inertia.
How many hours of sleep do I need?
Adults (18–64) generally need 7–9 hours per night, roughly 5–6 full cycles. Adults 65 and older need about 7–8 hours, teenagers 8–10 hours, and school-age children 9–11 hours. Needs vary by person, but consistently sleeping under 6 hours is considered insufficient long-term.
How long should a power nap be?
The most effective power nap is 10–20 minutes — short enough to avoid entering deep sleep, so you wake up alert without grogginess. Naps of 30–60 minutes can involve some deep sleep and brief grogginess on waking. A 90-minute nap completes a full cycle (including REM) with the least grogginess of the longer options.
How is a sleep cycle calculated?
You pick an anchor time — either when you want to wake up or when you're going to bed — then count 90-minute blocks backward or forward from it, adding roughly 15 minutes for the time it takes to fall asleep. Times that land on 4, 5, or 6 full cycles are recommended, with 5–6 cycles (7.5–9 hours) being ideal.
What time should I go to bed to wake up early?
Count back 5 or 6 full cycles from your target wake-up time and add your time to fall asleep. For example, to wake at 6:00 AM, go to bed at 10:15 PM for 5 cycles or 8:45 PM for 6 cycles. Going to bed and waking at the same time every day, getting morning sunlight, and reducing screens before bed also help.
What is sleep inertia?
Sleep inertia is the temporary grogginess, heaviness, and trouble concentrating you feel when you wake up in the middle of deep sleep. It can last from a few minutes to about half an hour. The 90-minute cycle method aims to time your wake-up for the lightest part of a cycle to reduce this effect.
What's the best time for a nap?
The best time for most people to nap is early afternoon, roughly between 1:00 and 3:00 PM. This lines up with a natural dip in alertness and doesn't interfere with nighttime sleep. Napping late in the day can make it harder to fall asleep at night, so it's best to keep naps to 20–30 minutes.
Does this tool store my data?
No. All calculations run entirely in your browser — the times you enter are never sent to a server. The only way your schedule becomes shareable is if you tap "Copy link," which encodes your inputs into a URL; sharing that link is entirely up to you.
What is a chronotype, and which one am I?
A chronotype is your body's natural tendency toward morning or evening activity, often grouped into four types: Lion (early riser, sharpest in the morning), Bear (follows the sun, most common type), Wolf (night owl, most alert in the evening), and Dolphin (light sleeper, easily disrupted). Take the 30-second chronotype quiz above to find yours and get a personalized tip.

Methodology & sources

ToolPico's Sleep Calculator is a free, independent tool. The calculation engine is based on: a full sleep cycle of 90 minutes, an average time to fall asleep of ~15 minutes (adjustable), and an ideal sleep target of 5–6 cycles (7.5–9 hours). Cycle-end times are found by counting 90-minute blocks backward from your wake-up time or forward from your bedtime; the math uses whole-minute arithmetic, including cases that cross midnight.

Sources: National Sleep Foundation age-based sleep recommendations, consistent with guidance from the CDC and the American Academy of Sleep Medicine · general scientific consensus on sleep physiology (sleep stages, REM, circadian rhythm). These are evergreen recommendations that don't change from year to year. Last updated: July 19, 2026. Results are for informational purposes only and are not medical advice.

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