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Sleep Tracking: Why You Should Focus Solely on Sleep Debt

When it comes to sleep tracking, forget “sleep quality” and sleep stages. Knowing your sleep debt score lets you take action for better sleep and better days.
Reviewed by
Jeff Kahn, M.S., Rise Science Co-Founder
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Man sleeping with sleep tracker

Waking up in the morning, you groggily check your Fitbit app on your iPhone to see how your sleep fared last night. A "Good" sleep score, with individual graphs for light sleep, deep sleep, and REM (rapid eye movement) sleep, seem to paint a picture of a good night's sleep.

Despite that, you feel like you lagged more than usual at work. You can't help but question if your Fitbit smartwatch is actually helping you reach your sleep goals or if you should make the switch to an Apple Watch. You might even wonder, "Does sleep tracking even work?"

The answer is, yes, sleep tracking does work in determining whether you've had enough sleep to help you feel and function well during the day. But, it's not about subjective parameters like "sleep quality" (which, by the way, has no scientifically agreed-upon definition) or scrutinizing how much time you've spent in REM sleep.

Instead, sleep debt (the amount of sleep you've missed out on in the past 14 days relative to your sleep need) is the only sleep-tracking metric that directly and profoundly impacts your daytime functioning. Keep reading to find out why this is the only sleep-tracking metric you should care about.

The No. 1 Pitfall of Most Sleep Trackers on the Market

Most sleep-tracking devices and apps on the market track your sleep duration without taking your biological sleep need into account. Sure, popular sleep-tracking wearables (think the Fitbit, Apple Watch, and the Ōura Ring) use fancy tools and technology like accelerometers and heart rate variability to feed their own algorithms.

Unfortunately, they miss the main point of sleep tracking right out of the gate. These gadgets fail to provide your individual sleep need, which is necessary to help you determine if you had enough sleep last night — or not.

Before you counter with, "But I clocked in eight hours last night," you should know that everyone has a sleep need that's genetically determined, just like eye color and height. While your partner may need 8.5 hours of sleep per night, you may actually need nine for optimal energy the next day.

In fact, research shows that the average sleep need is around 8 hours and 10 minutes (give or take 44 minutes). A not insignificant proportion of the population — roughly 13.5% — actually need nine hours or more to feel and function at their best (or as close to it as possible).

Sleep Debt — The Most Useful Sleep Score Out There

RISE app screenshot showing how much sleep debt you have
The RISE app uses the only sleep tracking metric that matters — sleep debt.

A sleep score is only useful if you can use it to tweak your daily routine to be at your best. This is where sleep debt trumps all other sleep-tracking metrics. It, with the right guidance (more on that later), is immediately actionable to help you achieve better sleep at night for better energy during the day and, in turn, enhance your overall health and reach your full potential in the long run.

Unfortunately, most sleep scores don't share how you can leverage them to optimize your daytime well-being performance. For example, Fitbit's sleep scoring system appears to be an opaque combination of sleep duration (seemingly unpegged to your biological sleep need), a stab at perceived sleep quality, and a dash of restorative metrics (like heart rate and restlessness).

Without the faintest idea of how your tracker calculates your sleep score, you’re obligated to put your faith in their algorithms, which shouldn't be necessary in the first place. Consequently, you won't know which metric to work on — or by how much — to improve your score. Would you have to extend your sleep duration? And how do you improve something as subjective as your "sleep quality"?

Instead of making strides toward your actual sleep goal of feeling and functioning better each and every day, you're only juicing a rather meaningless score that has no obvious or readily actionable impact on your daytime energy levels.

In contrast, RISE's sleep debt score is easy to understand and dictated by the science of sleep — not just a fancy proprietary algorithm we thought up. All you have to do is chip away at your sleep debt until it's less than five hours. You can achieve this by outsleeping your sleep need or by consistently meeting your sleep need for the next 14 nights. Sounds doable, right?

The Fallacies of Tracking “Sleep Quality” and Sleep Stages

Sleep tracking: person monitoring their sleep on their laptop and mobile

Contrary to popular belief, data about your "sleep quality" and the time you spent in each respective stage of sleep doesn't portray the true story of last night's sleep. The former is only subjective at best, while the latter is out of your conscious realm of control. Despite this, most consumer sleep-tracking wearables still obsess over these metrics.

There Is No Consensus on “Sleep Quality,” Even Among the Experts

What most people don't know is there’s currently no official definition of "sleep quality," as sleep scientists have yet to agree on an objective measurement for it. Even the gold standard Pittsburgh Sleep Quality Index is a (largely) subjective-based questionnaire comprising seven self-rated components.

Yet, how do most sleep trackers measure “sleep quality”? They simply base it on how much time you spent in each sleep stage and whether you’ve cycled through them as the night progresses. If you aren’t clear on the sleep cycle, here’s a recap: 

  • Stage 1: You experience light sleep. 
  • Stage 2: You experience deeper sleep.
  • Stage 3: You experience slow-wave sleep, also known as deep sleep.
  • Stage 4: You experience rapid eye movement (REM) sleep.

Take note that stages 1-3 are non-REM sleep. During the night, it’s normal to go through each sleep stage about 4-6 times.

But before you hold sleep staging to the highest esteem, you should know that the various stages of sleep are merely definitional constructs created in the 1940s and 1950s. In other words, they aren't based on math or fact, and are subjected to change with every new discovery. For example, recognizing REM sleep as a sleep stage in 1953 led to a facelift of the then-newly developed sleep scoring system.

In that sense, sleep trackers that devised their own definition of “sleep quality” based on sleep staging may not be wholly accurate.

Arguing against a non-existent "sleep quality" is, therefore, a non-sequitur. Yet, despite the fallacy of the definition itself, many people still believe that "sleep quality" is somehow defined by spending the "right" amount of time in certain stages of sleep, a perspective that the sleep science community certainly doesn't support.

We can look toward a 2014 study as proof. Participants who were told they had "experienced above average sleep quality" (they spent more time in REM sleep) had better cognitive performance despite their initial views on how well they had slept. Interestingly, the reverse rings true. You're more likely to perform badly when told you had below average "sleep quality," whether you had actually slept well or not.

The study's findings also suggest that the duration of each sleep stage doesn't impact how you feel and function the next day. Research conducted by sleep and machine learning scientists at Stanford University further backs this up. Even when these experts extracted all the best "sleep quality" data from lab-based sleep studies, they still can't predict how you'll feel in the morning.

The bottom line is, the only thing that imprints how you feel during daylight is how much sleep debt you're carrying.

Man-made Sleep Trackers Are Only Human

Man checking his wrist watch while lying in bed

Before you buy the next "it" fitness tracker, know that some of the best sleep trackers are vulnerable to the fallibility of tracking technology outside a sleep lab.

Currently, the only gold standard in sleep tracking is polysomnography (sleep study). It's a lab-based test used for sleep monitoring to assess your sleep patterns when diagnosing sleep disorders, like obstructive sleep apnea (OSA).

A polysomnogram measures various parameters, such as brain wave activity, heart rate, blood oxygen levels, and core body temperature. Due to its comprehensiveness, no test or tool outside of a sleep lab can replicate a polysomnogram's accuracy.

Keep in mind that sleep stage scoring, even when done in a lab, isn't an exact science. The sleep experts conducting them only agree with each other about 80% of the time!

This is why most consumer sleep-tracking devices are ineffective, even when they claim they can deliver lab-quality results in tracking your sleep cycle. If you're not connected to sensors and wires while you're in bed, the device or app is likely not tracking your sleep stages very precisely.

In fact, a 2020 study found that "there is a remarkably high degree of variability in the accuracy of commercial sleep technologies." Using Fitbit as an example, a 2019 study in the Journal of Medical Internet Research highlighted that the wearable tech's sleep app isn't "a substitute for PSG" (polysomnography), despite what the brand proclaims.

According to the study, sleep-staging Fitbit models (which measure body movement and heart rate variability) underestimated how much time you take to fall asleep (scientifically known as sleep latency). This suggests spillover inaccuracies to other sleep parameters like total sleep time and sleep efficiency (how much time you spent asleep in bed).

In other words, your "Good" sleep score on the Fitbit app and other trackers is likely not a true representation of your sleep last night and may, in fact, be worse than that. This is why, at Rise, we ipso facto don't track sleep stages because we don't want to contribute to the already burgeoning pile of sleep misinformation.

Sleep Stage Tracking Is Superfluous

Even if you could somehow track your sleep stages accurately outside of a sleep lab, there is nothing you can do with that data. What many people also don’t realize is, your brain already self-optimizes your sleep every night. It knows how much time to spend in every stage of sleep, from non-REM to REM and back again (we cycle through all sleep stages multiple times throughout the night).

Because you can't actively manipulate something as involuntary as sleep stage duration, having that information at your fingertips is superfluous. That said, certain daytime activities stymie your brain's naturalistic processes for sleep. For example, alcohol and caffeine consumption too close to your bedtime lowers REM sleep and deep sleep, respectively.

Instead of hamstringing your brain's built-in mechanisms, work with it by consistently meeting your sleep need.

We dive deep into why you can't sleep eight hours in four hours here.

RISE Can Help You Perfect Sleep Tracking the Right Way

Forget all the fancy gadgets that connect instantaneously with Wi-Fi, Bluetooth, and even Alexa. As we’ve mentioned, the only sleep metric worth scrutinizing is sleep debt.

But, tracking sleep debt only goes so far unless you have the tools to take control of it. This is where RISE can help. Using cutting-edge behavioral science, our app is pegged to your unique chronobiology to help you build healthy sleep habits.

RISE Makes It Easier for You 

RISE app screenshot showing your sleep need so you can track your sleep
The RISE app shows your sleep need that's unique to you.

From calculating your sleep need to measuring your sleep debt, the RISE app employs passive tracking in the background, so you don't have to lift a finger when it comes to your sleep data.

How it works:

  • Once you download the RISE app, it uses the past 365 days of sleep data stored in your phone to calculate your unique sleep need.
  • Every day, RISE leverages phone motion-based sleep detection to monitor the start and end of your sleep schedule and gauge your nighttime sleep duration. Weighing this number against your sleep need, RISE effectively calculates your sleep debt.

At Rise, we understand how difficult it can be to develop a new habit, much less stick with it. That’s why the RISE app is designed to eliminate all friction associated with your new healthy habit of sleep tracking.

Because our app lives on your phone, and even has a widget to let you access it directly on your phone's home screen, the information you need is always at your fingertips. Plus, you don't have to waste time or effort on keying in your sleep duration and tabulating your sleep debt. It's all done for you in the RISE app.

RISE Helps You Build Healthy Sleep Habits

Knowing your sleep debt is all very well and good. But to truly keep sleep deprivation at bay, good sleep hygiene is key. That's why the RISE app has 16 science-based habits with timely in-app notifications. Adding them to your Energy Schedule helps structure your day with sleep- and energy-promoting activities aligned with your circadian rhythm (your internal body clock).

With RISE, you'll never have to wonder when's the best time to wake up or go to bed. Nor do you have to question when to cut off your caffeine consumption or what time you should work out. For the full story on how to perfect your sleep hygiene, head over to our step-by-step Sleep Guide to learn more.

RISE Empowers You Every Day

We've shown you how the RISE app makes repeating healthy sleep habits seamless and effortless every day. But we also know the importance of empowerment in habit formation. After all, the more you enjoy doing something, the more likely you'll stick with the habit.

That's why RISE isn't just easy to use. It's empowering in a way that puts the reins of sleep tracking in your hands with the end goal of better sleep for better days. Case in point: Your sleep debt figure is intricately linked to your daily energy potential on the Sleep screen, with feel-good ratings like “Super” and “Great” for sleep debt below five hours.

Ready to feel and function at your best? Get the RISE app today.

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