How Do I Calculate My Sleep Cycle?

Count backward from your wake time in 90-minute blocks and add 30 minutes of buffer. Fifteen of those minutes are for falling asleep. The other fifteen are for the morning transition period during which you are technically a mammal but not yet a participating member of society. If your alarm is at 6:00am, subtract 15 minutes to get 5:45am, count back five 90-minute cycles to land on 10:15pm, then subtract the 15-minute falling-asleep buffer and you get a bedtime of 10:00pm.

If you followed that paragraph without difficulty, congratulations, you are not yet tired enough to need this website. Give it a few hours. And if you want to see this logic applied to a specific scenario, here is what happens when you sleep from 9:30 to 4:30 and why it feels the way it does.

Can I Do This Maths Myself Every Night?

You can, in the same way you can change your own oil or cut your own hair. The question is not whether it is possible but whether the results will be acceptable given the conditions under which you are performing the task. At 11pm, after a full day of work, your arithmetic skills have the structural integrity of a sandcastle at high tide.

The most popular mistake is forgetting the buffers entirely, which results in a bedtime calculation that assumes you fall asleep instantly and wake up like a robot powering on. You do neither of these things. Nobody does either of these things. The buffers exist because you are a human being and not a light switch, and the gap between intending to sleep and actually sleeping is filled with pillow adjustment, sudden thoughts about whether you locked the door, and one last look at your phone that lasts twenty minutes.

How Many Cycles Should I Aim For?

Five. This gives you 7.5 hours of actual sleep and positions your alarm at the end of a complete cycle, where your brain is practically holding the door open for you. Four cycles gives you 6 hours, which is the amount of sleep that keeps you technically operational in the way that a car with a cracked windscreen is technically operational. Legal, functional, and something you should really address before it becomes a larger problem. Three cycles gives you 4.5 hours, which we have labelled "Emergency" because it is, and pretending otherwise would make us complicit in whatever happens to you the following afternoon. This is precisely why we built the calculator.