What Time Should You Go to Bed? (By Wake-Up Time)
If you need to be up at 7:00 AM, go to bed by 9:45 PM for six full sleep cycles or 11:15 PM for five. Both land you between cycles instead of mid-cycle, which is what actually determines whether you wake up clear-headed or groggy, not just the total number of hours.
How sleep cycles work
A night of sleep isn’t one uniform block. It’s a series of repeating cycles, each lasting roughly 90 minutes, that move through light sleep, deep sleep and REM in sequence before starting over. You’ll typically run through four to six of these in a night, and each one does slightly different work: deep sleep dominates the earlier cycles and handles physical recovery, while REM stretches get longer toward morning and handle a lot of the mental processing.
The timing of when you wake up matters more than most people realize. Get pulled out of deep sleep partway through a cycle and you’ll feel that specific kind of grogginess, sometimes called sleep inertia, that no amount of coffee immediately fixes. Wake up at the boundary between two cycles, when your body has already shifted into lighter sleep, and the transition feels almost automatic.
There’s one more variable the calculator accounts for: falling asleep isn’t instant. Most people take around 15 minutes after getting into bed before they’re actually asleep, so the calculator adds that as a fixed buffer on top of the cycle math. It’s a small detail, but skip it and every suggested time is off by a quarter hour.
Bedtime by wake-up time
Here’s the full picture for the most common wake-up times, working backward through four different cycle counts.
| Wake-up time | 6 cycles (9h) | 5 cycles (7.5h) | 4 cycles (6h) | 3 cycles (4.5h) |
|---|---|---|---|---|
| 6:00 AM | 8:45 PM | 10:15 PM | 11:45 PM | 1:15 AM |
| 6:30 AM | 9:15 PM | 10:45 PM | 12:15 AM | 1:45 AM |
| 7:00 AM | 9:45 PM | 11:15 PM | 12:45 AM | 2:15 AM |
| 7:30 AM | 10:15 PM | 11:45 PM | 1:15 AM | 2:45 AM |
| 8:00 AM | 10:45 PM | 12:15 AM | 1:45 AM | 3:15 AM |
Every bedtime in that table already has the 15-minute fall-asleep buffer built in. So “10:15 PM” for a 6:00 AM wake-up at five cycles is when to be lying down with the lights off, not the moment you actually doze off.
Treat the 6-cycle and 5-cycle columns as the ones worth aiming for. Nine hours and 7.5 hours both sit inside the 7-to-9-hour range most adults need to function well. The 4-cycle and 3-cycle columns are there for reference, for the night you genuinely can’t avoid going to bed late, not as targets to plan around.
Worked example
Take the 7:00 AM row. Six full cycles means starting from 7:00 AM (420 minutes past midnight), subtracting the 15-minute buffer, then subtracting 6 x 90 = 540 minutes of sleep: 420 - 15 - 540 = -135, which wraps around to 9:45 PM the night before. That’s the first value in the row.
Five cycles repeats the same subtraction with a smaller block: 420 - 15 - 450 = -45, which wraps to 11:15 PM. Ninety minutes later to bed than the six-cycle option, ninety minutes less sleep, same principle.
You can run this for any wake-up time: take the time in minutes past midnight, subtract 15, then subtract 90 times however many cycles you’re aiming for, and wrap negative results by adding 24 hours’ worth of minutes (1440). It’s the same formula the calculator below runs automatically, in both directions.
Calculate with your own wake-up time
Enter any wake-up time (or bedtime) and get all four cycle options instantly, without doing the subtraction by hand.
Best times to go to bed
Based on 90-minute sleep cycles and about 15 minutes to fall asleep.
Common mistakes
Chasing a flat “8 hours.” Eight hours doesn’t divide evenly into 90-minute cycles, so an alarm set for exactly eight hours after you fall asleep has a real chance of going off mid-cycle. Rounding to 7.5 or 9 hours, five or six whole cycles, gets you a wake-up at a natural break point instead.
Ignoring the 15-minute buffer. If the table says 10:15 PM and you get into bed at 10:15 PM expecting to already be asleep, you’ve quietly shifted your whole schedule by a quarter hour without noticing. The suggested times are for lying down, not for being unconscious.
Treating 90 minutes as exact. It’s a population average, not a fixed unit that applies identically to everyone. Individual cycles commonly run anywhere from about 70 to 120 minutes, and they even shift somewhat across a single night. Use the calculator’s output as a strong starting estimate and adjust by 15 or 30 minutes if you consistently wake up groggy at the suggested time.
Assuming a short night is fine because it feels fine. Four or five hours of sleep can feel manageable in the moment, especially with caffeine covering the gap, but sleeping that little on a regular basis is linked to worse focus, worse mood and slower reaction time. The 4-cycle and 3-cycle columns above exist for the occasional late night, not as a sustainable routine.
Frequently asked questions
How long is one sleep cycle? About 90 minutes on average. Each cycle moves through light sleep, deep sleep and REM in order before the next one begins.
Why does the calculator add 15 minutes? Because falling asleep isn’t instant. Most people take roughly 15 minutes after getting into bed before they’re actually asleep, so that gets added as a buffer to every suggested bedtime.
How many hours of sleep do I actually need? Most adults do best on 7 to 9 hours, which works out to five or six full cycles. That’s why those two options are marked as recommended rather than the shorter ones.
Is 6 hours of sleep enough? Six hours is exactly four cycles, and it can get you through the occasional short night. Making a habit of it is a different story: consistently sleeping that little is associated with worse concentration and mood over time, so it’s better used as a fallback than a nightly target.
Can I share this tool with my times pre-filled? Yes. As you enter a wake-up time or bedtime, the page’s URL updates to match, so you can copy it straight from the address bar or use the Share button. Anyone who opens that link sees the same time and mode already set.