Sleep efficiency describes how much of a recorded sleep period was spent asleep rather than awake. It can add useful context when time in bed and time asleep tell different stories.
What the percentage means
Sleep efficiency is the percentage of the recorded period that the source classified as sleep. More recorded awake time produces a lower percentage.
It is not the same as total sleep. You can have a long sleep period with lower efficiency, or a shorter period with higher efficiency. Read both measurements together.
Where Zolt gets the data
Zolt uses the sleep and awake intervals supplied by your connected health platform. The phone or wearable estimates those intervals from its sensors and software. Zolt does not turn a wearable into a clinical sleep study.
This means an unusual percentage can reflect the night itself, the way the source marked the sleep period, or incomplete data.
How to interpret a change
Start with your own recent range instead of a universal cutoff.
- A one-night change may reflect normal variation.
- A repeated change can help you spot a pattern worth investigating.
- A large mismatch between how you feel and what the app shows is a reason to inspect the source record.
Use the stage and awake-time views to see what changed. Then consider ordinary context such as a different schedule, illness, travel, alcohol, a late workout, or a disrupted environment. The metric can reveal a relationship, but it cannot prove the cause.
If the result looks wrong
- Check the sleep period in Apple Health or your connected platform.
- Look for missing hours or a period split into separate records.
- Confirm that awake intervals are present.
- Check the wearable fit, battery, and sleep-tracking settings.
- Review Data Sources and Access if multiple apps write sleep data.
If the original record is incomplete, fix the source or its permissions first. If the original is correct and Zolt differs, contact support with the date and screenshots.
When the metric needs more context
Wearable estimates should not be used to diagnose insomnia, sleep apnea, or another condition. Speak with a healthcare professional if sleep problems persist, you regularly feel unrefreshed, or you experience excessive daytime sleepiness, loud snoring, or gasping during sleep.