AHI Calculator

1. Choose what you are reading. Pick a sleep study report if you have event counts and a time, or a CPAP report if your machine or app shows an AHI number. Say whether the person tested is an adult or a child.
2. Copy the numbers from the report. Enter the apneas and hypopneas (or one total), the total sleep time in hours or minutes, and whether it was an in-lab study or a home test. Add the hypopnea rule if the report names it.
3. Read the result with your report in hand. Check the events per hour, the adult band and the reading note, then take the report to your sleep doctor.

Not tested yet? This page interprets a number you already have. To check warning signs and risk factors before a test, use the sleep apnea risk calculator instead.

The AHI is the average number of apneas and hypopneas per hour of sleep. It is the main number a sleep study uses to grade obstructive sleep apnea in adults. Each event has to last at least 10 seconds to count.

• Apnea: breathing stops completely, or airflow drops below 10% of normal, for at least 10 seconds.
• Hypopnea: breathing becomes shallow, with airflow reduced by 30% or more for at least 10 seconds, plus an oxygen drop or an arousal under the scoring rule your lab uses.

These bands are for adults only. Children are judged with much lower cut-offs because even a few events can matter in a growing child, so this tool does not band a child result. For the condition itself, its symptoms and how it is diagnosed, read our sleep apnea guide.

The calculation is simple division. The judgement around it is not, which is why the tool adds notes instead of a diagnosis.

1. Add the events. Apneas plus hypopneas, or the single total from your report.
2. Convert the time. Minutes are divided by 60, so 372 minutes becomes 6.2 hours.
3. Divide and round. Events divided by hours, rounded to one decimal place. The band is read from the rounded value, so the number you see and the band always match.
4. Add the context. The tool labels a home result as REI, adds a note when recording time was short, and explains the effect of the hypopnea rule if your report names one.

In CPAP mode there is nothing to divide: the machine has already done it. The tool compares the residual AHI your machine reports with the under-5 level.

Imagine 100 breathing events in one night. In a lab, sensors show the person was asleep for 6.5 hours. A home device cannot measure sleep, so it divides by the full 7.5 hours of recording. The event count is kept the same here to show the effect of the denominator alone.

An hour awake in bed moved the result across a band line. That is why the Sleep Foundation says home tests often underestimate the AHI, and why your sleep doctor may weigh a borderline home result differently from a lab result.

The 3% vs 4% Hypopnea Rule

Labs do not all score hypopneas the same way. The American Academy of Sleep Medicine (AASM) recommends counting a hypopnea when airflow drops by 30% or more with either a 3% fall in blood oxygen or an arousal from sleep. The rule used by the US Centers for Medicare and Medicaid Services requires a 4% oxygen fall and ignores arousals. Any event that meets the 4% rule also meets the 3% rule, so the 3% rule can only count the same number of hypopneas or more. An AASM task force noted that some people meet the threshold for sleep apnea under the 3% rule but not the 4% rule.

Sleep Time vs Recording Time

A lab study measures sleep with brain-wave sensors. Most home tests do not, so they divide by the whole recording and report a respiratory event index (REI). A Mayo Clinic study of home tests found that at least 300 minutes of recording were needed for an accurate result.

Night-To-Night Change

The AHI is an average across one night. It hides hour-by-hour patterns and links between sleep position and events, and a single lab night may not reflect someone whose AHI changes from night to night.

When The Events Happen

The Sleep Foundation notes that many women have most of their events in REM sleep, which an average across the whole night can hide.

The ODI and the AHI measure different things, so they rarely match. This tool works out the AHI or REI; it does not combine them.

The usual reference point is under 5 events per hour. The Sleep Foundation reports that when people with severe sleep apnea use CPAP for at least six hours a night, their AHI returns to normal levels, below five events per hour. A residual AHI of 5 or more on your machine is a reason to show the data to your sleep doctor, not a reason to change settings yourself.

Look at the trend over a week or more instead of one night. If you want to understand the options your doctor may discuss, our sleep apnea treatment guide covers CPAP and the alternatives.

• Adults with a new sleep study report who want to see how the headline number was worked out before their follow-up visit.
• People who had a home test and want to understand why the number may read lower than a lab study.
• CPAP users reading the AHI on their machine or app.
• Partners and carers helping someone make sense of a report.

It is not a screening tool. Questionnaires used before testing, such as the one explained in why doctors recommend the STOP-Bang questionnaire, answer a different question: whether a test is worth doing.

Treating The Band As The Diagnosis

MedlinePlus says the sleep specialist also looks at the other study findings, your medical history and a physical exam before making a diagnosis and deciding on treatment.

Using Adult Bands For A Child

Children use different cut-offs. A child number that looks normal on the adult scale may not be.

Ignoring A Normal Number When Symptoms Continue

A low AHI does not show how long each event lasted or how low oxygen fell. If loud snoring or sleepiness continue, tell your doctor.

Assuming A High Number Means Nothing Is Wrong Because You Feel Fine

Untreated sleep apnea is linked to wider health problems; see sleep apnea health risks.

The arithmetic is exact for the numbers you enter. What it means for you depends on things only your full report and your doctor can show.

In adults, 12 events per hour falls in the mild band, which runs from 5 to 14. Whether it means sleep apnea for you is decided by your sleep specialist, who also looks at the rest of the study, your history and an exam.

Add the apneas and hypopneas and divide by the hours of sleep. For example, 90 events over 6 hours of sleep is 15 events per hour.

Fewer than 5 events per hour is considered normal for adults. Children use lower cut-offs.

Most home tests divide by recording time rather than sleep time, so time spent awake lowers the number. The Sleep Foundation says home tests often underestimate the AHI by about 15 percent.

No. It counts how often events happen, not how long each one lasted or how low oxygen fell. Those details are elsewhere in the report.

Not on its own. The Sleep Foundation warns that relying only on the AHI can overlook symptoms and health history, so the decision is made with your sleep doctor.

It will do the division, but it will not band a child result, because children are judged with much lower cut-offs. Discuss the report with the child’s sleep doctor.

It is the oxygen drop needed to count a shallow-breathing event. The AASM recommends 3% or an arousal; Medicare uses 4%, which counts fewer events.

No. It can change from night to night, so a single night in a lab may not match a typical night at home. Tell your sleep doctor if the result does not fit how you sleep or feel.

Show the machine data to your sleep doctor or equipment provider. Check the trend over several nights and do not change the settings yourself.

• Sleep Foundation: Apnea-Hypopnea Index (AHI) (definition, event rules, adult bands, home tests underestimate by about 15%, CPAP below five, children)
• MedlinePlus: Polysomnography (adult AHI bands; diagnosis also uses other findings, history and exam)
• Berry et al.: Transition to the AASM-recommended hypopnea definition in adults (J Clin Sleep Med, 2022; PMID 35197190) (3% or arousal rule vs 4% CMS rule)
• Wittine, Olson and Morgenthaler: Recording duration and out-of-center sleep testing (Sleep, 2014; PMID 24790276) (REI from total recording time; at least 300 min recording)