AHI Calculator - Apnea-Hypopnea Index
Enter the number of apnea events, hypopnea events, and your total sleep time to calculate your Apnea-Hypopnea Index (AHI). Your result is automatically classified as normal, mild, moderate, or severe using standard sleep medicine thresholds for adults and children, with a step-by-step breakdown of the math.
Formula
Worked example
A patient records 28 apneas and 32 hypopneas over 6 hours of sleep: AHI = (28 + 32) / 6 = 60 / 6 = 10 events/hr, which falls in the mild sleep apnea range for adults.
What is the Apnea-Hypopnea Index?
The Apnea-Hypopnea Index (AHI) is the standard metric used to quantify the severity of sleep-disordered breathing. It expresses how many times per hour a person's breathing is completely halted (an apnea) or significantly reduced (a hypopnea) during sleep. An apnea is defined as a cessation of airflow lasting at least 10 seconds with less than 10% of baseline airflow. A hypopnea is a partial obstruction lasting at least 10 seconds with at least 30% reduction in airflow. Both types disrupt normal sleep architecture and, when frequent, deprive the body and brain of oxygen. AHI is measured during a polysomnography (in-lab sleep study) or a home sleep apnea test, and the resulting score guides diagnosis and treatment decisions.
How this calculator works
Enter the total number of apnea events, the total number of hypopnea events, and the total sleep time recorded by your study. The calculator adds the two event counts, converts your sleep time to hours if you entered it in minutes, and divides to produce the AHI. It then compares your score against the standard American Academy of Sleep Medicine (AASM) thresholds and tells you whether the result falls in the normal, mild, moderate, or severe range. You can toggle between adult and pediatric thresholds because children are classified differently: even 1 event per hour is considered abnormal in a child, while adults are considered normal below 5.
AHI severity categories and what they mean
For adults, an AHI below 5 is normal. An AHI of 5 to 14 is mild obstructive sleep apnea (OSA), which is often managed with positional therapy, weight loss, or a mandibular advancement device. An AHI of 15 to 29 indicates moderate OSA, where continuous positive airway pressure (CPAP) therapy is typically the first-line recommendation. An AHI of 30 or higher is severe OSA, linked to significantly increased risk of hypertension, arrhythmia, stroke, and metabolic syndrome. CPAP therapy aims to reduce AHI below 5 events per hour (a "treated normal"). For children, thresholds are lower: mild is 1 to 4, moderate is 5 to 9, and severe is 10 or more events per hour.
What AHI does not capture
AHI counts events but not their severity. Two patients can have the same AHI while experiencing very different oxygen desaturations. The Oxygen Desaturation Index (ODI) complements AHI by tracking how often blood oxygen falls by 3-4% or more per hour. The Respiratory Disturbance Index (RDI) goes further and includes Respiratory Effort-Related Arousals (RERAs), brief events that fragment sleep without meeting the strict apnea or hypopnea criteria. Home sleep tests that record total recording time rather than actual sleep time underestimate AHI by roughly 15%, because the denominator is larger. Event frequency during REM sleep may carry greater cardiovascular risk than the same events during NREM sleep, but a plain AHI does not distinguish between the two. For all these reasons, AHI should be interpreted alongside oxygen saturation data, symptoms, and clinical judgment by a sleep medicine specialist.
AHI severity classification by age group
| AHI (events/hr) | Adult classification | Child classification |
|---|---|---|
| Less than 1 | Normal | Normal |
| 1 to less than 5 | Normal | Mild |
| 5 to less than 15 | Mild | Moderate-Severe |
| 15 to less than 30 | Moderate | Severe |
| 30 or more | Severe | Severe |
Standard thresholds from the American Academy of Sleep Medicine (AASM). Pediatric thresholds are lower because any disruption to normal sleep architecture is clinically significant during development.
Frequently asked questions
What is a normal AHI score?
For adults aged 18 and older, an AHI below 5 events per hour is considered normal. For children under 18, the threshold is lower: an AHI below 1 event per hour is normal. Any score above these levels warrants a conversation with a sleep medicine physician.
What is the difference between an apnea and a hypopnea?
An apnea is a complete or near-complete cessation of breathing, where airflow drops below 10% of baseline for at least 10 seconds. A hypopnea is a partial obstruction: airflow is reduced by at least 30% for at least 10 seconds, usually accompanied by a drop in blood oxygen or an arousal. Both disrupt sleep and count equally in the AHI formula.
How is AHI different from RDI?
The Respiratory Disturbance Index (RDI) includes all events that AHI counts (apneas and hypopneas) plus Respiratory Effort-Related Arousals (RERAs). RERAs are brief episodes of increased respiratory effort that cause an awakening but do not fully meet the apnea or hypopnea criteria. Because RDI casts a wider net, it is always equal to or higher than AHI. Some patients with a normal AHI but a high RDI still have clinically significant sleep-disordered breathing.
Why are pediatric AHI thresholds lower than adult thresholds?
Children are still developing neurologically and cardiovascularly, so even a small number of breathing events per hour can impair growth, behavior, cognitive function, and cardiovascular health. The American Academy of Pediatrics considers any AHI above 1 event per hour in a child to be abnormal, compared to the adult threshold of 5. Treatment (often adenotonsillectomy) is commonly recommended even for mild pediatric sleep apnea.
What AHI does CPAP therapy aim for?
The standard treatment goal for CPAP therapy in adults with obstructive sleep apnea is an AHI below 5 events per hour (a "treated normal"). Research shows that effective CPAP use of at least 6 hours per night can reduce AHI by around 73% on average. Your CPAP machine logs its own internal AHI each night, which your sleep team can download and review.
Can I use AHI from a home sleep test?
Home sleep tests provide a useful AHI estimate, but they typically measure total recording time rather than actual sleep time. Because most people are awake for some portion of the recording, the denominator is inflated and the resulting AHI is slightly underestimated - by roughly 15% compared to an in-lab study. This means a home test score at or near a threshold should be confirmed with an in-lab polysomnography for clinical decision-making.