How to read your sleep tracker's stage chart

What a 2025 laboratory comparison found

A March 22, 2025 study compared six wrist-worn trackers with laboratory polysomnography in 62 adults, including healthy people and patients with suspected sleep apnea. Each wore two to four devices for one night; 52 participants were men. (Tracker validation study)

The trackers recognized over 90% of lab-scored sleep periods but only about 29%–52% of wake periods. That first percentage describes sleep detection, not overall accuracy. Agreement across wake and sleep-stage categories was fair to moderate. (Tracker validation study)

Testing occurred in 2023–2024. One laboratory night, uneven device samples, missing recordings and changing algorithms limit application to current products. VLAIO funded the work; authors reported no financial affiliations or nonfinancial conflicts. (Tracker validation study)

Separate the stage chart from the score

The American Academy of Sleep Medicine's 2021 technology update explains that an overall sleep score can be a product-specific calculation. Stage labels can also differ between apps in their definitions, inputs and algorithms. A score and minutes assigned to a stage answer different questions. (AASM technology update)

Our practical interpretation: before comparing two screens, identify the exact metric and read each product's explanation. Check whether you are comparing minutes, percentages or a proprietary score. A higher number in one app is not automatically a better result than a lower number in another. Ask which specific output any validation claim covers. (AASM technology update)

Give the result a narrow description

Imagine that your app assigns fewer minutes to deep sleep after your first night on a different mattress. Start with a precise description: the app reported a different estimate that night. Then write down the separate observation you actually want to investigate, such as finding it awkward to turn or liking the new surface.

The timing of two events alone does not establish that one caused the other. You changed beds, and a number changed; that leaves the explanation open. Buying an accessory immediately would add another decision before you have identified the problem you want it to solve.

For a purchase decision, finish this sentence without using an app number: “I want my bed to feel or work differently in this way…” If you have a clear answer, you have a concrete shopping question. If you do not, give yourself room to consider what, if anything, you want to buy.

Ask what would support a mattress claim

If a seller uses a sleep chart to demonstrate a mattress benefit, ask for the complete comparison. Which mattress was tested, against what alternative, in how many people and for how long? Was the result measured with an independent method, and did the comparison account for other differences between the nights?

Keep the advertised benefit specific. Evidence about one person's comfort rating does not answer a claim about everyone gaining deep sleep. A screenshot with a favorable number is a starting point for questions; it does not supply the missing study design. Our temperature-controlled-cover article below illustrates how researchers can report different results for comfort ratings and recorded sleep.

Bring sleep concerns to the right conversation

NHLBI explains that common clinical sleep studies record brain waves alongside measures such as breathing, heart rate and blood oxygen. A clinician decides which testing is appropriate and interprets the results. That evaluation answers a different question from choosing a more comfortable bed. (NHLBI sleep studies)

If you seek help with sleep concerns, bring the app result as context alongside your own description of the problem. Explain what you noticed, when it began and what question you want answered. You do not need to turn the chart into a diagnosis before starting that conversation. (NHLBI sleep studies)