What time to sleep to wake up at 6:45 AM

If your alarm is set for 6:45 AM, here are the bedtimes that align with full 90-minute sleep cycles — so you wake up between cycles instead of in the middle of deep sleep.

6:45 AM is the “just enough time” alarm — popular with people on a tight but normal schedule who want to maximise sleep while still making a standard start. Every minute counts in a 6:45 morning, so the routine is usually efficient and well-rehearsed.

9:30 PM

6 cycles · 9 hours · Ideal

11:00 PM

5 cycles · 7.5 hours · Recommended

12:30 AM

4 cycles · 6 hours · Workable

2:00 AM

3 cycles · 4.5 hours · Short

Times assume ~15 minutes to fall asleep.

Why these specific times?

Your brain doesn’t sleep evenly. It cycles through stages of light sleep, deep sleep, and REM sleep. One full cycle averages 90 minutes. Waking up at the end of a cycle, during light sleep, feels effortless. Waking up mid-cycle — especially during deep sleep — leaves you groggy for an hour or more, a feeling sleep researchers call sleep inertia.

That’s why a 7-hour night sometimes feels worse than 6 hours: 7 hours can land you in the middle of a cycle, while 6 or 7.5 hours wake you up cleanly between cycles. If you need to be up at 6:45 AM, the bedtimes above let your last cycle end right around your alarm.

Making a tight morning work

At 6:45 the margins are thin, which makes hitting a clean sleep cycle especially valuable: waking groggy when your morning is already tightly packed sets a stressful tone for the whole day. Five full cycles puts your bedtime around 11:00 PM — a realistic, mainstream lights-out that fits an ordinary evening.

The single biggest upgrade for a 6:45 riser is cutting the snooze habit. Those extra nine-minute fragments after the alarm are shallow, non-restorative sleep that often leave you foggier than simply getting up — and in a tight morning you can’t afford the lost time anyway. Time your bedtime so your final cycle ends right around 6:45 and you’ll wake close to naturally, no snooze required.

How to pick the right bedtime

For most adults, the sweet spot is 5 cycles (7.5 hours). If you’re recovering from sleep debt, sick, doing intense physical training, or under 25, aim for 6 cycles (9 hours). Try to avoid 4 cycles or fewer unless you genuinely have no other option.

Tips to actually fall asleep at this time

Cool the room to 18–20°C (65–68°F). Your core temperature has to drop for sleep to start.
Kill the light. Even small amounts of light suppress melatonin — your body’s sleep signal.
Stop caffeine after 2 PM. Its half-life is 5–7 hours, so afternoon coffee is still active at midnight.
Cut screens 30 minutes before bed, or use night-mode filters. Blue light delays melatonin release.
Keep a consistent schedule, including weekends. Your circadian rhythm rewards regularity.

Need a different wake-up time?

Use the full sleep calculator to compute bedtimes for any wake-up time, or jump to another common time:

Go deeper

Want to understand the science behind these times? Read our in-depth guides:

About sleep cycles

The 90-minute cycle is an average, not a law. Real cycles vary from 70 to 120 minutes and shift throughout the night — early cycles contain more deep sleep, later cycles more REM. The calculator gives you a strong starting point, but you may need to adjust by 15–20 minutes after a few weeks of tracking how you feel.

If you struggle to fall asleep by the time recommended here, or wake up exhausted regardless of timing, this calculator can’t replace a conversation with a doctor. Persistent insomnia, daytime exhaustion, and snoring all deserve professional attention.