A typical sleep cycle — moving through light, deep, and REM sleep — lasts about 90 minutes. Waking up in the middle of one, especially during deep sleep, tends to feel groggier than waking up at the end of a cycle, even with less total sleep. Picking a bedtime by rounding to a convenient half hour ignores that entirely.
Bedtime calculator, working backward from a wake-up time
Enter when you need to wake up, and this calculator shows several bedtime options — each one landing you at the end of a full 90-minute cycle, with about 15 minutes added for the time it typically takes to fall asleep.
Wake up time calculator, working forward from now
Switch modes to go the other direction: enter when you're going to bed, and see wake-up times that each complete a full number of cycles (3 through 6) instead of an arbitrary round number of hours.
What time should I go to bed for 6 vs 8 hours
The options offered cover roughly 4.5 to 9 hours of total sleep across 3 to 6 cycles — this is a general guideline based on the average cycle length, not a personalized measurement of your actual sleep.
