Bedtime calculator
Plan bedtime or wake-up time around your sleep target and time to fall asleep.
Weekly sleep debt calculator
See how your last seven nights add up against the sleep you aim for.
Your seven nights
Example valuesEnter hours asleep. For example, 7.5 = 7h 30m.
No account needed. Calculations happen in your browser; your entries are not saved or sent to Century.
Example · Estimated weekly shortfall
6h 0m
5 of 7 nights fell below your target.
- Nightly average
- 7h 13m
- Nightly target
- 8h 0m
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How it’s calculated
For each night, shortfall = max(0, your target − actual sleep). We add those shortfalls across all seven nights. Longer nights appear in your average but do not cancel earlier shortfalls. Your target is an input, not a measured sleep need. This is a planning estimate, not a model of physiological recovery or a promise to repay sleep hour for hour.
Reference: NHLBI: Your guide to healthy sleep
For general wellness information. This tool does not diagnose health conditions or replace medical advice.
Related tools
Understand your weekly sleep shortfall
How to use the weekly sleep debt calculator
Choose a nightly sleep target, then enter your estimated hours asleep for each of seven completed nights. Use the same target throughout the week. Enter actual sleep rather than the time between getting into bed and getting out of bed.
Decimal hours make short intervals easy to enter: 6.5 is six hours and thirty minutes, and 7.25 is seven hours and fifteen minutes. Enter zero for a night with no sleep. A blank field means the week is incomplete, so the calculator waits before showing a total.
Why a long night does not cancel a short one
This tool adds only the positive shortfall on each night. If your target is eight hours, a six-hour night contributes two hours; a ten-hour night contributes no shortfall. The longer night still counts toward your nightly average.
That distinction matters: an average can hide a week that alternates between short and long nights. The NHLBI’s guide to healthy sleep explains that sleeping in on a weekend does not completely erase sleep debt. The calculator therefore does not promise a date when you will be fully recovered.
Turn the estimate into a clearer sleep log
The result depends on the target and sleep durations you enter. It cannot measure your personal biological sleep need or determine whether a wearable’s sleep estimate is accurate. If you change your target, the estimated shortfall changes too.
Use the seven-night view to identify the nights that repeatedly fall short of your own target. Keep your logging approach consistent when comparing one week with another. Century can bring available wearable sleep history and recovery signals together for a more continuous view.
Frequently asked questions
How do I calculate sleep debt for a week?
For each of seven nights, subtract actual sleep from your nightly target and count only positive shortfalls. Add those shortfalls to estimate weekly sleep debt. With an eight-hour target, three nights of seven hours and four nights of eight hours give a three-hour weekly shortfall.
Why is my sleep debt different from my average sleep?
Weekly sleep debt adds only nights below your target, while average sleep includes every night. With an eight-hour target, a six-hour night creates a two-hour shortfall and a ten-hour night creates none. Their average is eight hours, but this tool still reports two hours of shortfall.
What is sleep debt?
Sleep debt describes sleep missed relative to your sleep need. This tool estimates a seven-night shortfall against the personal target you enter. Actual sleep need varies, so the result depends on your chosen target.
Does sleeping longer on weekends erase sleep debt?
Extra sleep may help, but it does not guarantee that every effect of short sleep is reversed. This calculator keeps nightly shortfalls separate instead of treating a long night as an automatic repayment.
Should I enter time in bed or time asleep?
Enter estimated time asleep, excluding time spent awake in bed. Use decimal hours: 7.5 means 7 hours and 30 minutes; 7.25 means 7 hours and 15 minutes.
Is this the same as Century’s sleep debt score?
No. This free tool is a transparent snapshot of seven manually entered nights. Century uses available wearable history to provide ongoing sleep and recovery insights.