Sleep Calculator

What is this actually calculating?

Times that land at the end of a whole sleep cycle rather than in the middle of one. The tool models a cycle as 90 minutes and adds 14 minutes for falling asleep, then works backwards from your wake-up time or forwards from your bedtime for 3, 4, 5 and 6 cycles.

Why does it add 14 minutes?

Because you do not fall asleep the instant you lie down. That allowance — sleep latency — is built into every suggested time, so a bedtime the tool gives you is when to be in bed with the light off, not when you expect to be unconscious.

Why 90 minutes, and is that right for me?

Ninety minutes is the round figure commonly used for an adult cycle through light sleep, deep sleep and REM. Real cycles vary between people and across the night — they tend to run shorter early on, with REM taking a larger share towards morning. So treat these times as a useful approximation, not a schedule your brain is obliged to follow.

Why does waking mid-cycle feel so much worse?

Waking out of deep sleep produces sleep inertia — that heavy, disoriented state that can take a while to shake off. Waking at the end of a cycle, when sleep is lightest, generally feels easier. That is the whole idea behind aligning an alarm to cycle boundaries.

Which option should I choose?

Five cycles — about seven and a half hours of sleep — is highlighted as the default suggestion, and sits inside the range usually recommended for adults. Six cycles is nine hours. Three or four are there for nights when that is genuinely all the time you have, not as a target to aim for.

Is a shorter whole cycle better than more total sleep?

Not as a habit. Cycle alignment can make a given amount of sleep feel better on waking, but it does not replace the sleep itself. Consistently choosing four cycles over six because the maths looks tidy means accruing a deficit no alarm timing will fix.

Why do the suggested times ignore naps and my weekend schedule?

Because the tool only knows the one time you type in. It has no view of your wider sleep pattern, and going to bed at wildly different times each night affects how you feel more than landing on a cycle boundary does.

Does it store my times?

No. The calculation runs in your browser and nothing is saved or sent.

What if I sleep badly no matter what I do?

Timing arithmetic will not fix persistent insomnia, loud snoring with daytime exhaustion, or sleep that never feels restorative. Those are worth raising with a doctor — some have treatable causes that no calculator can address.