Calculate Apnea Hypopnea Index from total respiratory events or apnea and hypopnea counts plus sleep time, and see sleep apnea severity.
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Apnea Hypopnea Index Formula
The apnea hypopnea index, or AHI, is the number of apnea and hypopnea events per hour of sleep. The calculator can use either a single total event count or separate apnea and hypopnea counts.
Quick mode, using total respiratory events:
AHI = E / T
- AHI = apnea hypopnea index, in events per hour
- E = total respiratory events, meaning apneas plus hypopneas
- T = total sleep time in hours
Split mode, using apnea and hypopnea counts:
AHI = (A + H) / T
- AHI = apnea hypopnea index, in events per hour
- A = number of apnea events
- H = number of hypopnea events
- T = total sleep time in hours
If your sleep time is entered in minutes, the calculator first converts it to hours:
T = minutes / 60
The quick function is useful when your sleep report already gives the total number of respiratory events. The apnea plus hypopnea function is useful when your report lists those two event counts separately. In both cases, the result is divided by total sleep time so the final AHI is shown as events per hour.
AHI Severity Ranges
AHI is commonly grouped into severity categories based on events per hour of sleep.
| AHI result | Category | Meaning |
|---|---|---|
| Less than 5 | Normal | Below the usual clinical threshold for sleep apnea |
| 5 to less than 15 | Mild sleep apnea | Mild range of breathing interruptions during sleep |
| 15 to less than 30 | Moderate sleep apnea | Moderate range of breathing interruptions during sleep |
| 30 or higher | Severe sleep apnea | High frequency of breathing interruptions during sleep |
Example AHI Calculations
Example 1: Total events mode
You have 42 total respiratory events over 7 hours of sleep.
AHI = 42 / 7 = 6
The AHI is 6 events per hour, which falls in the mild sleep apnea range.
Example 2: Apnea plus hypopnea mode
You have 18 apnea events and 24 hypopnea events over 420 minutes of sleep.
T = 420 / 60 = 7
AHI = (18 + 24) / 7 = 6
The AHI is 6 events per hour, also in the mild sleep apnea range.
FAQ
What counts as an apnea or hypopnea event?
An apnea is a pause or near-pause in breathing during sleep. A hypopnea is a partial reduction in breathing that is usually paired with an oxygen drop or sleep disruption. Sleep studies count these events and use them to calculate AHI.
Is AHI the same as events per night?
No. AHI is events per hour, not total events for the whole night. For example, 40 events over 8 hours gives an AHI of 5, while 40 events over 4 hours gives an AHI of 10.
Can AHI diagnose sleep apnea by itself?
AHI is a key measurement, but diagnosis depends on the full sleep study and clinical context. Symptoms, oxygen levels, sleep position, sleep stage, and medical history can also matter. If your result comes from a home test or lab report, discuss it with a qualified clinician.
