Sleep Calculator - Bedtime

Sleep Calculator uses the idea that sleep runs in ~90-minute cycles (light → deep → REM) to find "refreshing" bed and wake times — timed so you wake at the end of a cycle, in light sleep, rather than mid-deep-sleep. See at a glance what time to wake if you sleep now, or what time to go to bed to hit a target wake-up.

■ Bed & wake calculation
· Sleep now? — enter your bedtime (or "now") to get recommended wake times at cycle ends.
· Wake by a set time? — enter your target wake time to get recommended bedtimes, worked backwards.
· "Today/tomorrow" labels with time remaining.
· Accounts for the time it takes you to fall asleep, so it calculates from when you actually doze off.
· Sleep cycle preview — a hypnogram visualizing the depth of the selected night.

■ Nap mode
· Wake times tuned for 10/20/30/60/90-minute power naps.
· One-tap alarm via your device's clock app.

■ Log & sleep debt
· Record a night by bed/wake times (with sleep quality and a note).
· Edit past entries, pick any date, period filters (7/14/30 days), search by note or date.
· Sleep debt dashboard — sleep below your goal over the last 7 days, average sleep, and goal streak.
· Last 14 nights bar chart (with a goal line).

■ Stats
· Bedtime regularity score, average sleep by weekday, average bed/wake times.
· Quality trend and a 10-week calendar heatmap to spot your pattern.

■ Reminders & extras
· Bedtime reminder — a local notification at the time you choose.
· Turn recommended bed/wake times into a shareable image card.
· Backup & restore your data (on-device file).
· First-run onboarding and a "tip of the day" in the Guide.

■ Guide
· Plain-language notes on sleep cycles, waking at a cycle's end, sleep debt, recommended sleep by age, and sleep hygiene.

■ Privacy & storage
· All records and settings stay only on your device (never uploaded).
· No account or login; works offline.
· Korean/English, light & dark themes.

Note: Ads include a bottom banner and rewarded ads. Watching a rewarded ad you choose can optionally unlock: remove the banner for 24h, detailed stats, theme skins, backup & restore, share skins, and premium presets.
Note: The recommended times and sleep debt are reference estimates from a general sleep-cycle model, not medical advice. Actual sleep varies by person and condition; if problems persist, consult a professional.