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.
Free · No sign-up · Built on 90-minute sleep cycles
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, so the clock starts after you're actually down.
Wake between cycles
Aim for a multiple of 90 from sleep onset, and the alarm lands while you're already near the surface.
Set it from either end
Tell it the time you have to be up, or the time you're heading to bed tonight. It counts in full cycles and gives you plain times to aim for.
Cycles average 90 minutes but drift a little night to night, so treat each time as a target window of ten minutes or so either side. The highlighted option is the usual sweet spot — long enough to feel rested, short enough to fit a normal night.
The wake windows that don't hurt
A real night isn't a smooth slope. Deep sleep stacks up early; REM stretches out toward morning. The surface moments between cycles are your friendly exits — that's what the calculator is aiming the alarm at.
A bedtime is only as good as your biology
This tool assumes two things: that you know roughly how much sleep you need, and that your body actually wants to sleep when you tell it to. Both are personal. If your schedule keeps fighting you, start one level up.
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 melatonin-free night drink 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 (Albion®) to take the edge off the racing-mind hour, L-Theanine and L-Glycine for calm without grog, and 5-HTP from Griffonia seed 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.
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 and isn't medical advice. Sleep needs and cycle lengths vary, and persistent trouble sleeping is worth a conversation with your doctor. These statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.