Sleep Cycle Calculator

Find a bedtime that suits your sleep cycles

Waking mid-cycle leaves you groggy, and timing sleep to complete cycles helps. This calculator suggests bedtimes based on your wake time and 90-minute sleep cycles.

Why sleep cycles matter for waking

Sleep runs in cycles of roughly ninety minutes, moving through light and deep stages, and waking at the end of a cycle, in light sleep, feels far better than waking mid-cycle in deep sleep, which causes grogginess. Working backward from your wake time in ninety-minute blocks suggests bedtimes that let you wake at the end of a cycle. The ninety minutes is an average, so it is a guide rather than exact, but timing sleep to cycles rather than a round number of hours is a genuinely useful trick.

A health estimate

This is an estimate from a standard formula for general information, not medical advice; individual health depends on far more than any single number, so consult a professional for anything that matters. It runs entirely in your browser, so nothing you enter is uploaded, keeping your figures on your own machine.

Related tools

• User Agent Parser — Parse a User-Agent string into browser, engine, operating system and device. Explains why UA strings are unreliable and what to use instead.
• QR Code Generator — Generate QR codes for URLs, text, Wi-Fi and contact details. Adjustable error correction and size, produced entirely in your browser.
• Credit Card Validator — Validate a card number with the Luhn algorithm and identify the issuing network from its prefix. Runs locally, nothing is transmitted.
• Text Case Converter — Convert text between camelCase, PascalCase, snake_case, kebab-case, CONSTANT_CASE, Title Case and sentence case. Runs entirely in your browser.