Free AHI Calculator | Apnea-Hypopnea Index
Enter your sleep data to see your AHI score
The Apnea-Hypopnea Index (AHI) calculator is a key resource for sleep apnea evaluation, often used together with the STOP-BANG questionnaire and the Epworth sleepiness scale to screen and classify the severity of breathing disruptions during sleep. This free AHI calculator online allows users to estimate their condition using the OSA AHI scale, though it is not a substitute for professional medical advice.
What Is the Apnea-Hypopnea Index?
The Apnea-Hypopnea Index measures the average number of abnormal breathing events per hour of sleep. Two types of events are counted:
- Apnea: a complete pause in airflow lasting at least 10 seconds.
- Hypopnea: a noticeable reduction in airflow amplitude, often accompanied by oxygen desaturation.
The AHI score is obtained by adding all apnea and hypopnea events together and dividing by the total hours of sleep.
Why AHI Matters
High AHI values are associated with an elevated risk of stroke, high blood pressure, heart attack, and Parkinson’s disease. Identifying and treating sleep apnea can help lower these risks and improve daily well‑being. Alongside AHI, other screening tools such as the STOP-BANG assessment and Epworth scale provide complementary information about risk factors and daytime sleepiness.
AHI and Obstructive Sleep Apnea (OSA)
OSA occurs when throat muscles relax excessively, blocking the airway during sleep. The AHI score is essential for diagnosing OSA and determining its severity. A continuous positive airway pressure (CPAP) machine delivers pressurised air to keep the airway open. Tracking AHI changes over time can indicate how well CPAP therapy is working for mild, moderate, or severe cases.
How to Calculate AHI
The calculation involves three steps:
- Sleep monitoring – A sleep study records breathing patterns, identifying apneas (breathing pauses >10 s) and hypopneas (shallow or slow breathing).
- Counting events – The total number of apnea and hypopnea episodes is tallied.
- Applying the formula – The AHI is computed as:
If sleep time is recorded in minutes, use:
Interpreting the AHI Scale
Sleep apnea severity is categorised as follows:
| AHI (events per hour) | Classification |
|---|---|
| 0–4 | Normal |
| 5–14 | Mild sleep apnea |
| 15–29 | Moderate sleep apnea |
| 30+ | Severe sleep apnea |
These thresholds guide treatment decisions, which may include lifestyle adjustments, oral appliances, or CPAP therapy. Using this sleep apnea severity calculator provides an initial indication, but a complete diagnosis should be made by a sleep specialist.
FAQ
1. How is the AHI score calculated?
Take the total number of apnea and hypopnea events during sleep and divide by the number of hours slept. If sleep time is in minutes, multiply the event count by 60 and then divide by sleep minutes: AHI = (apnea + hypopnea) × 60 / sleep time (minutes).
2. What do the different AHI scores mean?
0–4 is considered normal, 5–14 indicates mild sleep apnea, 15–29 moderate sleep apnea, and 30+ severe sleep apnea. This classification helps guide treatment options such as CPAP therapy.
3. Can I use an AHI calculator to monitor CPAP treatment?
Yes. Tracking AHI over time while using a CPAP machine shows whether the therapy is keeping breathing events within a normal range. A score of 5 or higher may indicate that the treatment needs adjustment.
4. What is the difference between apnea and hypopnea?
Apnea is a complete pause in breathing for at least 10 seconds. Hypopnea is a significant reduction in airflow (often with oxygen desaturation) rather than a full stop. Both events are counted together to calculate the AHI.
How to Use
- Enter the number of apnea episodes and hypopnea episodes recorded during your sleep study.
- Enter the total actual sleep time and select the appropriate time unit (hours, minutes, or seconds).
- Your AHI score and sleep apnea severity interpretation will be calculated automatically in real-time.