Sleep Calculator

Find possible bedtimes for a wake-up time, or wake-up times for a bedtime, using approximate 90-minute sleep cycles and your time to fall asleep. Options for 4, 5 and 6 cycles in 12- or 24-hour time.

Health & Fitness Runs client-side Free to use

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About the Sleep Calculator

Sleep Calculator suggests bedtimes or wake-up times based on approximate 90-minute sleep cycles. Choose “I need to wake up at” to get possible bedtimes, or “I plan to go to bed at” to get possible wake-up times. The tool adds your estimated time to fall asleep (15 minutes by default, and you can change it) and lists options for 6, 5 and 4 cycles with the estimated sleep and total time in bed.

Times that cross midnight are handled correctly, and you can show them in your device’s format, 12-hour or 24-hour time. The 90-minute cycle is an approximation — real cycles vary and sleep needs differ between people — so the results are general information only. The tool cannot diagnose sleep problems or guarantee better sleep; for ongoing sleep difficulties, consult a qualified healthcare professional.

How to use

Choose “I need to wake up at” or “I plan to go to bed at”.
Enter the time.
Adjust how long it usually takes you to fall asleep (default 15 minutes).
Choose 12-hour, 24-hour or your device’s time format.
Click Calculate, then copy the schedule or download the summary.

Key features

Two modes: plan a bedtime or plan a wake-up time.
Options for 6, 5 and 4 approximate 90-minute cycles.
Editable time to fall asleep (0–120 minutes).
Correct handling of times that cross midnight, with day labels.
12-hour, 24-hour or device time format.
Copy Schedule, Download Summary, Reset and Back.

Best practices

Keep a regular sleep and wake time, including at weekends where you can.
Be honest about how long you take to fall asleep.
Pick the option that fits your life, not just the most cycles.
Notice how rested you feel and adjust over a week or two.
Talk to a healthcare professional about persistent sleep problems.

Benefits

Quickly see sensible bedtime or wake-up options.
Accounts for the time it takes to fall asleep.
Easy to copy into notes or a calendar.
Private — works entirely in your browser.

Frequently asked questions

How does the sleep calculator work?

It counts back (or forward) in 90-minute sleep cycles from the time you enter and adds your time to fall asleep. For example, waking at 07:00 with 6 cycles and 15 minutes to fall asleep gives a bedtime of 21:45.

Are sleep cycles really 90 minutes?

Roughly. Cycles typically last somewhere around 70–120 minutes and vary through the night and between people, so 90 minutes is an approximation.

How many cycles should I aim for?

The tool shows 6, 5 and 4 cycles (9, 7.5 and 6 hours of sleep). Many adults are advised to get around 7 or more hours, but needs vary — choose what helps you feel rested.

Does it handle times after midnight?

Yes. If a suggested bedtime falls on the previous day or a wake-up time on the next day, it is labelled accordingly.

Can it diagnose sleep problems?

No. It is a planning aid only and cannot diagnose sleep disorders or guarantee better sleep. If you have ongoing trouble sleeping, loud snoring or daytime sleepiness, consult a qualified healthcare professional.

Can I use 24-hour time?

Yes. Choose 12-hour, 24-hour or your device’s own format; the copied schedule uses the same format.