AHI Calculator - Free Online Tool

Calculate your Apnea-Hypopnea Index and sleep apnea severity using AASM guidelines

Welcome to our free AHI Calculator, a comprehensive tool that helps you understand your Apnea-Hypopnea Index — the primary metric used by sleep medicine specialists to diagnose and classify the severity of sleep apnea. Whether you have recently completed a sleep study and want to interpret your results, or you are monitoring the effectiveness of your CPAP therapy, this calculator provides detailed analysis based on official American Academy of Sleep Medicine (AASM) guidelines. The Apnea-Hypopnea Index, commonly abbreviated as AHI, measures the average number of breathing interruption events per hour of sleep. These events fall into two categories: apneas, which are complete cessations of airflow lasting at least 10 seconds, and hypopneas, which are partial reductions in airflow of 30% or more for at least 10 seconds, often accompanied by a drop in blood oxygen saturation or an arousal from sleep. By combining these two event types and dividing by the total hours of sleep, the AHI gives clinicians a standardized, comparable measure of sleep-disordered breathing severity. Sleep apnea is one of the most prevalent yet underdiagnosed medical conditions worldwide. It is estimated that over 900 million people globally have obstructive sleep apnea (OSA), with a significant proportion remaining undiagnosed and untreated. Untreated sleep apnea does far more than cause daytime fatigue and snoring. Research published in major medical journals has linked chronic untreated OSA with significantly elevated risks of hypertension, heart attack, stroke, type 2 diabetes, metabolic syndrome, depression, cognitive impairment, and motor vehicle accidents. Epidemiological data indicates that approximately 70% of patients who experience a myocardial infarction and 65% of stroke patients have concurrent sleep apnea with an AHI greater than 10. Our calculator supports both adult and pediatric thresholds, reflecting the fundamental differences between how sleep apnea presents and is classified in children versus adults. For adults, the AASM defines a normal AHI as fewer than 5 events per hour, mild sleep apnea as 5 to 14.9 events per hour, moderate sleep apnea as 15 to 29.9 events per hour, and severe sleep apnea as 30 or more events per hour. Pediatric thresholds are significantly stricter, recognizing that even a single apneic event per hour can have measurable developmental and cardiovascular consequences in a child. For children under 13, normal is defined as fewer than 1 event per hour, mild as 1 to 4.9, moderate as 5 to 9.9, and severe as 10 or more events per hour. Beyond the basic AHI score, our tool provides several important supplementary outputs. You will see a breakdown of apnea events per hour and hypopnea events per hour separately, giving you a clearer picture of which event type dominates your sleep-disordered breathing pattern. The results include an oxygen saturation reference table based on clinical data, showing the typical SpO2 ranges associated with each severity level: normal AHI correlates with 96 to 97% oxygen saturation, mild with 90 to 95%, moderate with 80 to 89%, and severe with below 80%. This reference helps contextualize the physiological impact of each severity level. The CPAP effectiveness tracker is one of our most powerful differentiating features. If you are already on CPAP therapy, you can enter both your pre-treatment AHI (from your diagnostic sleep study) and your current CPAP-treated AHI to calculate your improvement percentage and assess whether your therapy is achieving its targets. Clinical research has demonstrated that effective CPAP therapy reduces AHI by approximately 73% on average. The treatment goal for CPAP therapy is an AHI of fewer than 5 events per hour, regardless of the original pre-treatment severity. All inputs accept decimal values, supporting the precision of modern sleep study reporting. The sleep time unit toggle allows you to enter your total sleep time in either hours or minutes, with automatic conversion displayed in the results. A visual severity gauge shows exactly where your AHI falls on a color-coded scale, making it easy to understand your position relative to all severity thresholds at a glance. The event breakdown chart visualizes the proportion of apnea versus hypopnea events contributing to your total score. An important note on test methodology: home sleep tests (Level III diagnostic devices) are known to underestimate AHI by approximately 15% compared to in-laboratory polysomnography (Level I), because home tests cannot directly measure total sleep time and instead use total recording time in the denominator. If your AHI was measured during a home sleep test, your true laboratory AHI may be somewhat higher. Additionally, AHI can vary significantly from night to night in the same individual, which is why clinical guidelines recommend evaluating AHI trends over multiple nights rather than relying on a single test result. This tool is for educational and informational purposes and is not a substitute for professional medical diagnosis or treatment planning.

Understanding the Apnea-Hypopnea Index

The Apnea-Hypopnea Index is the standard clinical metric for diagnosing and grading sleep apnea severity. It quantifies how often breathing is disrupted during sleep, combining complete cessation events (apneas) and partial reduction events (hypopneas) into a single hourly rate.

What Are Apneas and Hypopneas?

An apnea is a complete cessation of airflow lasting 10 or more seconds. In obstructive sleep apnea, the airway physically collapses due to relaxed throat muscles, blocking airflow entirely despite continued breathing effort. In central sleep apnea, the brain temporarily fails to send signals to the respiratory muscles, causing breathing to stop. A hypopnea is a less severe event: a partial reduction in airflow of 30% or more for at least 10 seconds, typically accompanied by either a 3-4% drop in blood oxygen saturation or an arousal from sleep recorded by EEG. Both event types fragment sleep architecture, prevent restorative deep sleep, and create cyclical drops in blood oxygen that strain the cardiovascular system. The 10-second minimum duration distinguishes pathological events from normal brief breathing variations that occur in all people during sleep.

How AHI Is Calculated

The AHI formula is straightforward: add the total number of apnea events to the total number of hypopnea events recorded during the sleep study, then divide by the total sleep time expressed in hours. The result is the average number of events per hour. For example, if a polysomnography records 30 apnea events and 20 hypopnea events during 6 hours of actual sleep, the AHI would be (30 + 20) / 6 = 8.3 events per hour, which falls in the mild category for an adult. Sleep time used in the calculation should always be actual sleep time verified by EEG-recorded sleep stages, not the total time spent in bed or total recording time. Home sleep tests often use recording time instead, which artificially lowers the AHI by 10-20% compared to laboratory studies.

Clinical Significance of AHI Severity

The AHI severity classification guides treatment decisions. A normal AHI of under 5 in adults requires no intervention for sleep-disordered breathing alone, though clinical judgment may differ if symptoms are present. Mild sleep apnea (5-14.9) is often managed with lifestyle modifications such as weight loss, positional therapy to avoid sleeping on the back, alcohol restriction before bed, and nasal decongestants. CPAP therapy may be recommended for mild OSA if the patient has significant symptoms or comorbidities such as hypertension. Moderate sleep apnea (15-29.9) typically warrants CPAP therapy, which is the gold standard first-line treatment with strong evidence for reducing cardiovascular risk and improving daytime function. Severe sleep apnea (30+) requires prompt treatment due to the significant cardiovascular and metabolic risks associated with chronic oxygen deprivation and sleep fragmentation. The OSA diagnosis threshold is AHI of 15 or higher, or 5 to 14 with documented symptoms including excessive daytime sleepiness, witnessed apneas, or comorbid hypertension, cardiac disease, or stroke history.

Limitations of AHI as a Metric

While AHI is the clinical standard, it has recognized limitations. AHI counts events but does not capture their duration, depth of oxygen desaturation, or the degree of sleep disruption each event causes. Two patients with the same AHI may have vastly different oxygen nadir values and arousal responses, leading to different symptom profiles and cardiovascular risk levels. AHI also does not account for Respiratory Effort-Related Arousals (RERAs), which are breathing events that cause arousal without meeting full apnea or hypopnea criteria. The Respiratory Disturbance Index (RDI) includes RERAs and is always equal to or greater than AHI, capturing a broader range of sleep-disordered breathing. AHI shows significant night-to-night variability in many patients, sometimes varying by a full severity category. A single sleep study may not represent the patient's typical sleep pattern. For this reason, clinical guidelines recommend considering multiple nights of data when possible and always interpreting AHI in the context of symptoms, comorbidities, and overall clinical picture.

AHI Calculation Formulas

Apnea-Hypopnea Index (AHI)

AHI = (Total Apneas + Total Hypopneas) / Total Sleep Time (hours)

The primary sleep apnea severity metric. Counts complete breathing cessations (apneas) and partial reductions (hypopneas) per hour of verified sleep time.

Respiratory Disturbance Index (RDI)

RDI = (Apneas + Hypopneas + RERAs) / Total Sleep Time (hours)

A broader metric than AHI that also includes Respiratory Effort-Related Arousals (RERAs). RDI is always equal to or greater than AHI for the same patient.

CPAP Improvement Percentage

Improvement % = ((Pre-treatment AHI − CPAP AHI) / Pre-treatment AHI) × 100

Measures the effectiveness of CPAP therapy by comparing pre-treatment AHI from the diagnostic sleep study to the current treated AHI. Clinical average improvement is approximately 73%.

AHI Severity Classification Tables

Adult AHI Severity Classification (AASM Guidelines)

Standard severity thresholds for adults per the American Academy of Sleep Medicine, with associated typical oxygen saturation ranges and recommended treatments.

Severity	AHI Range	Typical SpO2	Recommended Treatment
Normal	< 5 events/hr	96–97%	No treatment for SDB; address symptoms if present
Mild	5 – 14.9 events/hr	90–95%	Weight loss, positional therapy, oral appliance; CPAP if symptomatic
Moderate	15 – 29.9 events/hr	80–89%	CPAP therapy strongly recommended; cardiovascular risk management
Severe	≥ 30 events/hr	< 80%	CPAP therapy required; urgent evaluation for cardiovascular comorbidities

Pediatric AHI Severity Classification (AASM Guidelines)

Severity thresholds for children under 13 years. Pediatric thresholds are significantly stricter than adult thresholds because even mild sleep-disordered breathing can impact development.

Severity	AHI Range	Clinical Significance
Normal	< 1 event/hr	No clinically significant sleep-disordered breathing
Mild	1 – 4.9 events/hr	Evaluate for adenotonsillar hypertrophy; consider ENT referral
Moderate	5 – 9.9 events/hr	Adenotonsillectomy often indicated; monitor growth and behavior
Severe	≥ 10 events/hr	Prompt surgical intervention and/or CPAP; risk of developmental delay

AHI Calculation Examples

Adult AHI Calculation from Sleep Study

A polysomnography records 45 total events (28 apneas and 17 hypopneas) during 6 hours of EEG-verified sleep.

Total events = 28 apneas + 17 hypopneas = 45

Total sleep time = 6 hours

AHI = 45 / 6 = 7.5 events per hour

Severity classification: Mild (AHI 5–14.9)

Apnea events/hour = 28 / 6 = 4.7

Hypopnea events/hour = 17 / 6 = 2.8

Typical SpO2 for mild severity: 90–95%

Treatment: Lifestyle modifications (weight loss, positional therapy); CPAP if symptomatic or comorbidities present

AHI = 7.5 events/hr — Mild sleep apnea. Apneas dominate (62% of events). Lifestyle changes recommended; CPAP if symptoms persist.

CPAP Effectiveness Tracking

A patient diagnosed with severe OSA (pre-treatment AHI 42) has been using CPAP for 3 months. Current CPAP AHI is 3.8 events/hr.

Pre-treatment AHI = 42 events/hr (severe)

Current CPAP AHI = 3.8 events/hr

Improvement = ((42 − 3.8) / 42) × 100 = 91.0%

CPAP AHI of 3.8 is below the treatment target of 5 events/hr

Treatment target: MET (AHI < 5)

This 91% improvement exceeds the clinical average of ~73%

CPAP AHI = 3.8 events/hr — Treatment target MET. 91% improvement from pre-treatment AHI of 42 (severe → normal range).

Home Sleep Test with Underestimation Warning

A home sleep test records 55 events over 8 hours of recording time (not verified sleep time).

Total events = 55, Recording time = 8 hours

Reported AHI = 55 / 8 = 6.9 events/hr (mild)

Home tests use recording time, not actual sleep time

Estimated actual sleep time ≈ 8 × 0.85 = 6.8 hours (typical 15% awake time)

Adjusted AHI estimate = 55 / 6.8 = 8.1 events/hr (still mild, but higher)

If near a threshold, lab polysomnography recommended for confirmation

Reported AHI = 6.9 events/hr (mild). True AHI may be ~8.1 due to home test underestimation. Lab confirmation recommended for borderline results.

How to Use This AHI Calculator

Select Patient Type and Enter Event Counts

Choose whether you are calculating for an adult or a child under 13. Then enter the total number of apnea events and hypopnea events recorded during your sleep study. These numbers come from your polysomnography (PSG) report or home sleep test results. Apnea events are complete breathing cessations lasting 10+ seconds; hypopnea events are partial reductions in airflow of 30% or more lasting 10+ seconds with associated oxygen desaturation or arousal.

Enter Total Sleep Time

Input your total sleep time using either hours or minutes — toggle the unit to match your report. Use actual verified sleep time from your sleep study report, not time in bed or recording time. For polysomnography, sleep time is determined by EEG monitoring. Entering recording time instead of sleep time will underestimate your true AHI. Typical adult sleep study recordings last 7-8 hours, but actual sleep time may be 5-7 hours.

Review Your AHI Score and Severity Classification

Your AHI is calculated instantly and displayed with its severity category based on AASM guidelines. Review the severity gauge to see where your score falls on the Normal-Mild-Moderate-Severe scale. Check the calculation breakdown for apnea events per hour, hypopnea events per hour, and total event breakdown. Read the clinical interpretation and treatment recommendation for your severity level, and review the oxygen saturation reference associated with your classification.

Use CPAP Tracker to Monitor Treatment Progress

If you are on CPAP therapy, enable the CPAP Effectiveness Tracker by toggling the option below the main inputs. Enter your pre-treatment AHI from your diagnostic sleep study and your current CPAP-treated AHI from your titration study or CPAP device reporting. The calculator will show your improvement percentage and whether you have met the treatment target of AHI under 5 events per hour. Use Export CSV to save your results for tracking over time or sharing with your doctor.

Frequently Asked Questions

What is a good AHI score?

For adults, an AHI below 5 events per hour is considered normal with no clinically significant sleep-disordered breathing. An AHI of 5 to 14.9 indicates mild sleep apnea, 15 to 29.9 indicates moderate sleep apnea, and 30 or above indicates severe sleep apnea. For people on CPAP therapy, the treatment target is typically an AHI below 5, regardless of the original pre-treatment severity. Some specialists aim for an even lower treated AHI of under 2 events per hour for optimal symptom control. For children, thresholds are much stricter — a normal AHI is under 1 event per hour, and even mild elevations should prompt evaluation by a pediatric sleep specialist, because children are more sensitive to the developmental impacts of sleep-disordered breathing.

How does AHI differ from RDI?

AHI (Apnea-Hypopnea Index) counts only apnea and hypopnea events per hour. RDI (Respiratory Disturbance Index) is a broader metric that adds Respiratory Effort-Related Arousals (RERAs) — events where increased breathing effort causes a brief arousal from sleep without meeting the full criteria for an apnea or hypopnea. Because RDI includes more event types, it is always equal to or greater than AHI. A patient can have a normal AHI but an elevated RDI, indicating Upper Airway Resistance Syndrome (UARS), which causes daytime sleepiness and fragmented sleep despite a low AHI. If you have significant symptoms but a borderline or normal AHI, ask your sleep specialist whether your RDI was also measured and reported.

Why might my home sleep test AHI be lower than my lab AHI?

Home sleep tests (also called Level III portable monitoring devices) use total recording time as the denominator for AHI calculation, because they cannot verify actual sleep time without EEG monitoring. In-laboratory polysomnography uses EEG-verified actual sleep time, which is always shorter than recording time since you are not sleeping every minute you are in bed. Because dividing by a larger number produces a smaller result, home test AHI values are typically 10 to 15% lower than the AHI that would be measured for the same patient in a laboratory. If your home test result is near a threshold — for example, 4.5 or 14 events per hour — your true severity category may actually be one level higher. Sleep specialists are trained to account for this difference when interpreting home sleep test results.

Does AHI vary from night to night?

Yes, significantly. AHI can vary from night to night in the same individual due to several factors. Body position during sleep greatly affects OSA severity — sleeping on your back typically worsens AHI compared to sleeping on your side. Alcohol consumption within 4 hours of bedtime increases muscle relaxation in the throat, raising AHI. Nasal congestion from allergies, colds, or inflammation can worsen both apneas and hypopneas. Sleep stage distribution matters too: REM sleep is associated with lower muscle tone and typically produces more apneas than non-REM sleep. Fatigue, stress, and even the unfamiliar environment of a sleep lab can alter sleep patterns. For these reasons, some specialists recommend multiple nights of monitoring to get a representative AHI, especially when the first-night result falls near a severity threshold. Some CPAP devices track nightly AHI, allowing patients to monitor variability over time.

What CPAP AHI should I aim for?

The standard clinical treatment target for CPAP therapy is an AHI below 5 events per hour, which corresponds to the normal range on the adult severity scale. Most guidelines define effective CPAP therapy as achieving an AHI below 5. However, many sleep specialists and patients aim for even lower values — below 2 events per hour — for maximum symptom relief, particularly for individuals with severe daytime sleepiness or significant cardiovascular risk factors. Research has demonstrated that effective CPAP therapy reduces AHI by approximately 73% on average. If your treated AHI remains above 5 despite consistent CPAP use, you should contact your sleep medicine provider to evaluate mask fit, pressure settings, device type (CPAP vs. auto-titrating APAP vs. BiPAP), and underlying factors such as positional apnea or central events that may require a different treatment approach.

What are the health risks of untreated sleep apnea?

Untreated obstructive sleep apnea carries substantial long-term health risks beyond daytime fatigue and poor sleep quality. The repetitive cycles of oxygen desaturation and sleep arousal create chronic cardiovascular stress. Studies have linked untreated OSA with a significantly elevated risk of hypertension — up to 37% of OSA patients have difficult-to-control high blood pressure. Approximately 70% of patients who experience a heart attack and 65% of stroke patients have concurrent sleep apnea with AHI above 10. Type 2 diabetes risk is increased by insulin resistance caused by chronic sleep deprivation and intermittent hypoxia. Cognitive impairment, including memory problems and reduced executive function, is strongly associated with moderate to severe untreated OSA. Additionally, untreated sleep apnea dramatically increases the risk of motor vehicle accidents due to excessive daytime sleepiness — some studies estimate the risk is 2.5 to 7 times higher than in the general population.