Sleep Duration Calculator (Time Version)

Sleep duration calculator for bedtime and wake time across midnight

This sleep duration calculator is built for one specific job: you know the time you went to bed and the time you woke up, and you want a clean, accurate sleep duration. It handles the common real world situation where bedtime is late and wake time is the next morning. If your wake time is earlier than your bedtime, the calculator automatically treats the wake time as the next day.

The default view is intentionally simple. Enter bedtime and wake time using 24 hour time (for example 23:15 and 06:45). You will get the total time between those two times, shown as hours and minutes. This is your time in bed, which is the starting point for understanding how long you had available for sleep.

If you want a more realistic estimate of actual sleep, open the Advanced section. You can subtract a typical time to fall asleep (sleep latency) and any time you were awake during the night. Many people care about sleep opportunity (time in bed) and sleep time (time actually asleep). This calculator can show both, without forcing you to track every detail. If you do not know the advanced values, leave them blank and the calculator will still give a valid answer.

The output is designed to be practical, not academic. First, you get time in bed. Then you get an estimated sleep duration after adjustments. You also get a simple comparison against a target sleep value (default 8 hours unless you change it). Finally, if you provide a target, the calculator estimates a recommended bedtime for your chosen wake time, including your optional adjustments. This is useful when your wake time is fixed but your bedtime is flexible.

Assumptions and how to use this calculator

• Times are interpreted in 24 hour format (HH:MM). Single digit hours like 7:05 are allowed and treated as 07:05.
• If wake time is earlier than bedtime, the calculator assumes you woke up the next day, not earlier the same day.
• Sleep latency and time awake during the night are optional adjustments. If left blank, they are treated as 0 minutes.
• Estimated sleep duration is never allowed to go below 0. If adjustments exceed time in bed, the estimate is set to 0 and shown clearly.
• The recommended bedtime is a planning aid based on your target sleep plus your optional adjustments. It is not a medical recommendation.

Common questions

Why is my wake time treated as the next day?

If your wake time is earlier than your bedtime (for example 23:30 to 06:30), it almost always means you slept past midnight. The calculator assumes the wake time is the following day to avoid a negative or tiny duration.

What is the difference between time in bed and sleep duration?

Time in bed is the full window from bedtime to wake time. Sleep duration is the amount of that window you were likely asleep. If you take time to fall asleep or wake up during the night, your sleep duration can be lower than your time in bed.

What should I enter for time to fall asleep if I do not track it?

Leave it blank for a time in bed calculation, or use a rough estimate you believe is typical for you, such as 10 to 30 minutes. The calculator is designed to work even if you do not know this value.

What if I woke up multiple times and do not know the total awake time?

Leave the field blank if you do not know. If you want a better estimate, think in total minutes awake across the night and enter that total, even if it is approximate. The result will still be useful for comparing nights.

Can this calculator handle naps or daytime sleep?

Yes, as long as you enter a bedtime and wake time. If the wake time is later than the bedtime, it treats it as the same day. If it is earlier, it treats it as the next day. The logic is time based, not tied to night sleep only.