Free tool , sleep
Sleep cycle calculator.
Waking up groggy often means your alarm went off in the middle of a sleep cycle. Cycles run about 90 minutes, so timing your sleep in whole cycles can help you wake feeling clearer. Tell us when you need to be up, or when you are heading to bed, and we will suggest the best times. Everything runs in your browser, nothing is saved or sent anywhere.
How sleep cycles work
Across a night you move through repeating cycles of light sleep, deep sleep, and REM, each lasting roughly 90 minutes. Waking at the end of a cycle, when sleep is lightest, tends to feel far easier than being pulled out of deep sleep. These suggestions also add about 15 minutes for the time it usually takes to drift off, so the cycle counts line up with when you actually fall asleep.
One more thing that helps the whole night: caffeine has a half-life of around 5 to 6 hours, so a meaningful amount is still in your system long after the cup. A safe default is to finish your last coffee about 8 to 10 hours before bed.
This is general information about sleep timing, not medical advice. If you have ongoing sleep problems, talk to a clinician.
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