AHI (Apnea-Hypopnea Index)
Calculate your Apnea-Hypopnea Index (AHI) to assess sleep apnea severity. Enter apnea episodes, hypopnea episodes, and sleep time for results with severity classification and charts.
About This Calculator
What is the Apnea-Hypopnea Index (AHI)?
The Apnea-Hypopnea Index (AHI) is the standard medical metric used to diagnose and classify sleep-disordered breathing. It quantifies the average number of apnea (complete breathing pauses) and hypopnea (shallow breathing) events per hour of sleep. Developed from research in sleep medicine over the past four decades, the AHI is the primary endpoint used in sleep studies and CPAP therapy monitoring worldwide. Sleep physicians in India, the United States, and the United Kingdom all rely on the AHI to determine whether a patient has obstructive sleep apnea (OSA) and to what degree.
How is AHI Calculated?
The AHI calculation is straightforward: AHI = (Total Apnea Episodes + Total Hypopnea Episodes) / Total Sleep Time (hours). For example, if a patient experiences 50 apnea events, 30 hypopnea events, and sleeps for 8 hours, their AHI would be (50 + 30) / 8 = 10.0 events/hour. Apnea is defined as at least 90% reduction in airflow for 10 seconds or more. Hypopnea is defined as at least 30% reduction in airflow for 10 seconds or more, accompanied by 3–4% oxygen desaturation or an arousal. The American Academy of Sleep Medicine (AASM) recommends these scoring criteria, which are followed by sleep centers globally.
Clinical Significance and Treatment
A normal AHI (under 5 events/hour) typically requires no treatment based on the index alone, though symptoms like excessive daytime sleepiness warrant further evaluation. Mild sleep apnea (AHI 5–14) may be managed with lifestyle modifications, oral appliances, or CPAP depending on symptoms and comorbidities. Moderate sleep apnea (AHI 15–29) usually warrants CPAP therapy, which has strong evidence for reducing cardiovascular risk and improving quality of life. Severe sleep apnea (AHI 30+) requires prompt treatment — typically CPAP therapy, and in some cases of central sleep apnea, adaptive servo-ventilation (ASV) or BiPAP. Treatment decisions should always factor in symptoms (Epworth Sleepiness Scale score), oxygen desaturation nadir, and comorbidities.
Regional Notes
India: Sleep medicine is a growing specialty with accredited sleep labs at AIIMS New Delhi, Apollo Hospitals, Medanta, and other major institutions. The Indian Sleep Disorders Association promotes standardized AHI scoring. CPAP therapy is widely available through medical equipment providers. Health insurance coverage for sleep studies and CPAP varies — some policies cover diagnostic testing but not device costs. The rising prevalence of obesity in urban India has increased the burden of OSA.
United States: The AASM sets the standard for sleep study scoring and CPAP management. Medicare and most private insurers cover polysomnography and CPAP for patients with AHI of 15+ or AHI of 5+ with significant comorbidities. CPAP compliance data (usage over 4 hours/night for 70% of nights) is required for continued coverage. Home sleep apnea tests (HSAT) are increasingly used as a more accessible first-line diagnostic tool.
United Kingdom: NHS sleep services provide diagnostic sleep studies and CPAP initiation for patients with moderate-to-severe OSA. NICE guidelines recommend CPAP for symptomatic OSA with AHI of 15+ or AHI of 5+ with cardiovascular comorbidities. NHS England commissions sleep services through regional sleep centers. Private sleep studies are also available through hospitals like The London Sleep Centre.
Important Disclaimer
This calculator provides reference information only and is not a substitute for professional medical advice. A formal sleep study (polysomnography or home sleep apnea test) is required for accurate diagnosis. Results should be reviewed by a qualified sleep medicine specialist. Always consult a healthcare professional for diagnosis and treatment of sleep disorders.
Frequently Asked Questions
What is AHI (Apnea-Hypopnea Index) and why is it important?
AHI (Apnea-Hypopnea Index) measures the average number of apnea and hypopnea events per hour of sleep. It is the primary metric used worldwide — including India, the United States, and the United Kingdom — to diagnose and classify obstructive sleep apnea (OSA) severity. An AHI below 5 is considered normal, 5–14 indicates mild sleep apnea, 15–29 moderate, and 30 or more severe. Understanding your AHI helps determine appropriate treatment options such as CPAP therapy, oral appliances, or lifestyle modifications.
How is AHI calculated?
AHI is calculated by dividing the total number of apnea and hypopnea events by the total sleep time in hours. Apnea is defined as a complete cessation of airflow for 10 seconds or more, while hypopnea is a significant reduction in airflow (typically 30–50%) accompanied by oxygen desaturation or arousal. The formula is: AHI = (Apnea Episodes + Hypopnea Episodes) / Sleep Time (hours). For example, 20 apnea events and 15 hypopnea events over 7 hours of sleep yields an AHI of 5.0 events/hour.
What are the AHI severity categories?
The AHI severity categories are universally standardized: Normal (AHI 0–4.9, no treatment needed based on AHI alone), Mild Sleep Apnea (AHI 5–14.9, CPAP or oral appliance may be considered based on symptoms), Moderate Sleep Apnea (AHI 15–29.9, CPAP therapy typically recommended), and Severe Sleep Apnea (AHI 30+, CPAP strongly recommended; BiPAP may be considered for central sleep apnea). These thresholds are used by clinicians in India, the US, and the UK for diagnosis and treatment planning.
Can I use this AHI calculator for diagnosis?
No. This AHI calculator is for educational and reference purposes only. A formal sleep study (polysomnography or home sleep apnea test) is required for accurate diagnosis. The calculator provides an estimate based on user-reported event counts, which may differ from clinical scoring. Always consult a qualified sleep medicine specialist for diagnosis and treatment. In India, sleep studies are available at AIIMS, Apollo, and other major hospital networks. In the US, the American Academy of Sleep Medicine (AASM) accredits sleep centers. In the UK, NHS sleep services provide diagnostic testing.
What are the risk factors for a high AHI score?
Common risk factors for elevated AHI and sleep apnea include: obesity (BMI over 30), male sex, family history of sleep apnea, large neck circumference (over 40 cm or 16 inches), being over 40 years old, use of alcohol or sedatives before sleep, smoking, nasal congestion or obstruction, and medical conditions such as hypothyroidism, acromegaly, and polycystic ovary syndrome (PCOS). In India, increasing obesity rates and undiagnosed sleep apnea are significant public health concerns. The US and UK also see high prevalence of OSA, with an estimated 25% of men and 10% of women affected.
What is the difference between apnea and hypopnea?
Apnea refers to a complete pause in breathing for at least 10 seconds, during which airflow stops entirely. Hypopnea refers to a partial reduction in airflow (usually 30% or more) lasting at least 10 seconds, accompanied by a decrease in blood oxygen saturation (typically 3–4%) or an arousal from sleep. Both events are counted in the AHI calculation, but hypopnea scoring criteria can vary slightly between the AASM (US) and alternative scoring rules used in some sleep centers worldwide. This calculator uses the standard combined count.
How does CPAP treatment affect AHI?
CPAP (Continuous Positive Airway Pressure) therapy is the gold-standard treatment for obstructive sleep apnea. Effective CPAP treatment typically reduces AHI to below 5 events/hour (normal range). A CPAP machine's efficacy is measured by the residual AHI — the number of events that still occur despite therapy. An AHI of 5 or more on CPAP indicates that the therapy settings may need adjustment, such as increasing pressure, changing mask type, or addressing mask leaks. Most modern CPAP machines report AHI data directly to patients and their sleep specialists in India, the US, and the UK.
What is the difference between OSA, CSA, and mixed sleep apnea?
Obstructive Sleep Apnea (OSA) is caused by physical blockage of the upper airway due to relaxed throat muscles and soft tissue collapse. Central Sleep Apnea (CSA) occurs when the brain fails to send signals to the breathing muscles, with no physical obstruction. Mixed Sleep Apnea (also called complex sleep apnea) is a combination of both types. The AHI calculation alone cannot distinguish between these types — polysomnography with EEG monitoring is required. However, the AHI remains the primary severity metric for all types. Treatment differs: CPAP for OSA, adaptive servo-ventilation (ASV) or BiPAP for CSA.