Sleep Lab · Calculator

What time should you actually go to bed?

You can spend eight hours in bed and still wake up wrecked. Usually it's not the hours — it's where in the cycle your alarm caught you. Work back from when you need to be up, and land your wake-up in the gap between cycles instead of the middle of one.

Find my bedtime

Free · No sign-up · Built on 90-minute sleep cycles

Why timing beats hours

Sleep runs in cycles, not a flat block

Across the night you move through roughly five 90-minute cycles, each one dropping from light sleep down into deep sleep and back up toward the surface. Wake at the top of a cycle and you feel clear. Wake mid-deep-sleep and you get that drugged, can't-form-a-sentence feeling — even on a full night.

One cycle ≈ 90 minutes

Light to deep to REM and back. Five or six of them is a normal night.

Add time to fall asleep

Most people take around 15 minutes to drop off. The cycle clock starts after you're actually asleep.

Wake between cycles

Aim for a multiple of 90 from sleep onset, and the alarm lands while you're already near the surface.

The calculator

Set it from either end

Tell it when you need to be up, or when you're heading to bed. It counts in full cycles and gives you plain times to aim for.

What time do you need to wake up?

How fast do you fall asleep?

Cycles average 90 minutes but drift a little night to night — treat each time as a target window of ten minutes either side. The highlighted option is the usual sweet spot.

What a night actually looks like

The wake windows that don't hurt

Deep sleep stacks up early; REM stretches toward morning. The surface moments between cycles are your friendly exits — that's what the calculator is aiming the alarm at.

Easy to wake — near the surface Rough to wake — deep sleep

Where Moongreens fits

Hitting the schedule is the hard part

The maths is easy. Lying there wired at 11pm, or surfacing at 3am and not getting back down, is what wrecks the plan. That's the gap Moongreens was built for — a night drink with no added melatonin that supports your own wind-down so the bedtime you calculated is one you can actually keep.

It leans on named clinical forms rather than a sedative hit: KSM-66® Ashwagandha and Magnesium Bisglycinate Chelate to take the edge off the racing-mind hour, L-Theanine and L-Glycine for calm without grog, and Griffonia seed extract (a natural source of 5-HTP) to support your body's own melatonin pathway. No hormone, nothing to leave you groggy through the wake window you just worked out. Made in the USA.

Try Moongreens

90 nights, money-back. Sleep on it for three months. If it isn't working, you don't pay.

This calculator is for general guidance only and isn't medical advice. Sleep needs and cycle lengths vary — persistent trouble sleeping is worth a conversation with your doctor.

Questions

The honest answers

Is the 90-minute cycle exact?

No, and any tool that pretends it is, is overselling. Ninety minutes is the average; real cycles run anywhere from about 80 to 120 minutes, and your first cycle is often the shortest. That's why the calculator gives you a target time, not a to-the-minute command. Treat each result as a ten-minute window, and over a week or two you'll notice which one your body likes best.

Should I pick more cycles or fewer?

Five cycles — roughly seven and a half hours — suits most adults and is highlighted by default. Six gets you closer to nine hours if you're catching up or training hard. Four (about six hours) is a survival option for an early start, not a habit. The right number is whatever leaves you genuinely rested without an alarm dragging you out.

What if I can't fall asleep at the time it gives me?

Then the bedtime isn't the problem — the wind-down is. Two usual culprits: caffeine still circulating from the afternoon, or a nervous system that hasn't downshifted. The caffeine and alcohol calculator handles the first. For the second, a consistent wind-down routine and a night drink with no added melatonin are aimed squarely at the racing-mind window.

Does waking between cycles matter more than total sleep?

Both matter, and they're not in competition. Total sleep sets how recovered you are; cycle timing sets how you feel in the first thirty minutes after the alarm. You want enough hours and a clean exit. The calculator gives you both at once rather than trading one for the other.

Keep going

Hit the schedule, then hold it

The usual reason a good bedtime won't take is still in your system — the afternoon coffee or the evening glass of wine. Find out exactly what's working against tonight.

Caffeine & alcohol

The afternoon coffee and the evening glass of wine are the usual reasons a good bedtime won't take. Find out what's still in your system at lights-out.

Need to work out how much sleep to target? ← How much sleep you need