Sleep science, explained plainly
Sourced articles on sleep cycles, sleep inertia, and the everyday habits that affect how you sleep — each one linked back to the research behind it.
Free Printable Seven-Day Sleep Diary
Record bedtime, time awake and morning notes. Print a blank sheet or use our online weekly tracker.
Sleep basicsHow Many Hours of Sleep Do You Actually Need? (By Age)
A full breakdown of CDC and AASM sleep-duration guidance from infancy through older adulthood, and how to translate hours into full sleep cycles.
Sleep scienceThe Science of Sleep Cycles: What Happens Every 90 Minutes
Light sleep, deep sleep, and REM sleep explained stage by stage, and why timing your wake-up to a cycle boundary matters.
Sleep scienceWhy You Wake Up Tired Even After a Full Night's Sleep
The research behind sleep inertia, the groggy in-between state after waking, and what actually helps it pass faster.
HabitsBlue Light and Sleep: What the Research Really Shows
How evening screen use affects melatonin and sleep onset, according to controlled studies — and what the evidence doesn't yet prove.
Sleep healthSigns You Might Have a Sleep Disorder (And When to See a Doctor)
Warning signs of insomnia, sleep apnea, restless legs syndrome, and other common sleep disorders, based on guidance from Mayo Clinic and Cleveland Clinic.
Teen sleepSleep Calculator for Teens: Bedtime & Wake-Up Guide
Use a sleep calculator for teens to plan bedtimes and wake-up times around the 8–10 hours generally recommended for ages 13–17.
Sleep scheduleWhat Time Should I Go to Bed? Wake-Up Time Chart
Work backward from a 5, 6, 7 or 8 AM alarm. Compare 7–9 hours of sleep, allow time to fall asleep, and build a bedtime you can repeat.
Sleep habitsHow to Fix an Inconsistent Sleep Schedule
A practical guide to making an inconsistent sleep schedule more regular without chasing a perfect bedtime overnight.
Sleep durationIs 6, 7, or 8 Hours of Sleep Enough?
Is 6, 7, or 8 hours of sleep enough? Compare common sleep durations with current adult sleep guidance and individual variation.
Sleep scienceREM Sleep Explained: What It Is and When It Happens
REM sleep explained in plain language: where it fits in the sleep cycle, how it changes across the night, and why calculators cannot predict it exactly.
Sleep scienceDeep Sleep Explained: What Happens in NREM Stage 3
Learn what deep sleep is, where NREM stage 3 fits in the night, and why a bedtime calculator cannot measure your actual deep sleep.
Sleep basicsSleep Debt Explained: Can You Catch Up on Lost Sleep?
Sleep debt is the gap that builds when you repeatedly get less sleep than you need. Learn what catching up can and cannot do and how to rebuild a steadier routine.
Sleep basicsSleep Latency: How Long Should It Take to Fall Asleep?
Learn what sleep latency means, why a 15-minute fall-asleep buffer is only an estimate, and when persistent difficulty falling asleep is worth discussing with a professional.
Sleep scienceCircadian Rhythm Calculator: What It Can and Cannot Tell You
A circadian rhythm calculator cannot measure your body clock. Learn how to plan a consistent sleep schedule and track the difference between timing and duration.
NapsNap Length Guide: 20, 60 or 90 Minutes?
Compare common nap lengths, when shorter or longer naps may feel different, and why naps should not replace adequate nighttime sleep.
Sleep habitsHow to Wake Up Feeling More Refreshed
Wake up tired even after sleeping? Learn how sleep duration, consistency, sleep inertia and morning light can affect how refreshed you feel.
Sleep durationBedtime by Age: How to Plan Sleep Around Wake-Up Time
A practical bedtime-by-age guide that starts with recommended sleep duration and works backward from the time you need to wake up.