Sleep Calculator - Find your optimal wake-up time using 90-min sleep cycles

Sleep Calculator helps you wake up feeling refreshed by calculating optimal wake-up times based on 90-minute sleep cycles. Each sleep cycle consists of light sleep, deep sleep, and REM sleep — waking up at the end of a cycle (rather than in the middle) is the key to avoiding morning grogginess. The tool includes both "Sleep Now" and custom bedtime modes, plus a reverse calculator that tells you when to go to bed if you need to wake up at a specific time. Free, no sign-up required. Features: • Instant wake-up time calculation based on current time or custom bedtime • Reverse bedtime calculator (set your wake-up goal, get recommended bedtimes) • Sleep quality assessment tools • Science-backed blog articles on sleep health • Mobile-friendly, no app install needed