# The 3% Rule vs the 4% Rule for Sleep Apnea

1. The 3% rule counts a shallow breath when your oxygen drops 3% or the breath wakes your brain for a moment. Sleep doctors recommend it.
2. The 4% rule counts the same breath only when oxygen drops 4%. A brief wake up does not count. Medicare uses this rule to decide if it pays for CPAP.
3. One night can get two very different scores. In a Swiss study of 2,162 adults, the middle score was 10.1 events an hour on the 3% rule and 4.4 on the 4% rule.
4. Women lose the most under the 4% rule. In a Detroit sleep center, the 3% rule found 30.4% more cases in women and 21.7% more in men.
5. Ask your lab which rule your report used. If your plan wants the 4% rule, ask for the 3% count too.

Published October 22, 2026 by NightWells. General information, not medical advice.

Contents

This page is general information. It is not medical advice. Only your doctor can read your sleep study and tell you what it means for you. Do not stop or change CPAP or any other treatment on your own. If you have chest pain, signs of a stroke or severe trouble breathing, call 911.

Most people think a sleep study gives one fixed number. It doesn’t. Your score depends on which rule the lab used to count shallow breaths, and the two rules in use today can turn one night into two different answers. 1

We wrote this for anyone holding a sleep study report with a score near 5 or 15. Those are the lines where the rule can flip the result, and where insurance decides whether it pays.

## What Each Rule Counts

A sleep study counts two kinds of breathing events. An apnea is when air stops for at least 10 seconds. A hypopnea is a shallow breath, where airflow drops by at least 30% for at least 10 seconds. 8 Your AHI, the apnea hypopnea index, is the number of both per hour of sleep.

Apneas are easy to agree on. The fight is over which shallow breaths count. A shallow breath that doesn’t change much on its own only counts if something else happens with it. That something is what the two rules disagree on.

|  | The 3% rule | The 4% rule |
|---|---|---|
| Name in the scoring manual | Rule 1A, the recommended rule | Rule 1B, the optional rule |
| Airflow drop | At least 30% for 10 seconds | At least 30% for 10 seconds |
| Oxygen drop needed | 3% or more | 4% or more |
| Does a brief wake up count? | Yes, on its own | No |
| Who uses it | Sleep doctors, by the AASM’s advice | Medicare and many insurance plans |

The American Academy of Sleep Medicine, the AASM, made the 3% rule its recommended rule. Its scoring manual changed on February 15, 2023, and kept the 4% rule as an optional one. 1 The AASM had already said in 2018 that labs should count shallow breaths that end in a wake up, because those breaths cause real symptoms even when oxygen barely moves. 2

### What is the 3% rule for sleep apnea?

It’s a scoring rule. A shallow breath counts as a hypopnea when oxygen drops at least 3% or the breath ends in a brief wake up seen on the brain wave sensors. 2 Because more breaths qualify, your AHI comes out higher than it would on the 4% rule.

### What is the 4% rule for sleep apnea?

It’s the stricter rule. A shallow breath counts only when oxygen drops at least 4%, and a wake up alone doesn’t count. Medicare’s CPAP policy is written on this rule. 8

*Image. A blue finger pulse oximeter on a fingertip showing 96 percent oxygen and a pulse of 85*

A finger clip reading 96. During a shallow breath, a fall to 93 can count under the 3% rule. The 4% rule needs a fall to 92 or lower. Photo by [Stefan Bellini](https://commons.wikimedia.org/wiki/File:Pulox_Pulse_Oximeter.JPG), [CC0](https://creativecommons.org/publicdomain/zero/1.0/).

## How Far Apart the Two Scores Land

This is not a rounding error. The gap is large enough to move people across the lines doctors and insurers use, at 5 and 15 events an hour. Each study below scored the same recordings with both kinds of rule.

| Study | Who | What changed |
|---|---|---|
| HypnoLaus, Switzerland, 2019 3 | 2,162 adults from the general public, tested at home with full sensors | Middle AHI 10.1 on the 3% rule, 4.4 on the 4% rule. A score of 15 or more in 36.6% of people on the 3% rule and 18.8% on the 4% rule |
| Detroit sleep center, 2025 7 | 431 patients, every study scored both ways | Average AHI 34.7 on the 3% rule and 21.9 on the 4% rule. Cases rose 30.4% in women and 21.7% in men on the 3% rule |
| Mayo Clinic, 2024 6 | 76 lab studies, scored both ways | The 3% AHI ran about 8.6 events an hour higher than the 4% AHI, in every age group |
| Finland, 2015 5 | 68 patients with home recordings | A score of 15 or more in 29.4% of patients at a 4% oxygen drop and 73.5% at a 3% drop |
| Australia, 2009 4 | 328 lab patients | About 40% of people who had tested positive on the older, looser rule tested negative on the 4% rule |

The Finnish study shows the oxygen part alone does a lot of the work. It didn’t add wake ups at all, and still moved most of its patients into a worse group. Adding wake ups, as the full 3% rule does, pushes scores up more.

Who gets missed is not random. The Detroit team found the 4% rule mostly misses mild and moderate cases in women. 7 Its authors say the 4% rule may leave women with symptoms undiagnosed and untreated. A study of 1,201 people tested with a ring device found the two rules agreed less and less as age went up. 9

### Is a sleep apnea score of 3 considered high?

No. An AHI of 3 is under 5, which is the lowest line used in the studies above and in Medicare’s policy. 8 But check which rule produced it. A 3 on the 4% rule can be a much higher number on the 3% rule, and the Swiss data put the middle gap at more than double. 3

## Why Medicare Uses the 4% Rule

Medicare wrote its CPAP rule in 2008, and it still counts only 4% shallow breaths. The policy covers CPAP for claims on and after March 13, 2008. 8 It defines a hypopnea as at least a 30% drop in breathing for 10 seconds with at least a 4% oxygen drop.

### What AHI do you need for Medicare to cover CPAP?

Medicare covers a first 12 weeks of CPAP for adults when the AHI is 15 or more. It also covers it when the AHI is 5 to 14 and your record shows daytime sleepiness, trouble thinking, mood problems or insomnia, or shows high blood pressure, heart disease or a past stroke. 8 Both numbers mean the 4% rule. CPAP keeps being covered only if it helps you in those first 12 weeks.

Two of the contractors that handle Medicare equipment claims spelled it out for doctors. Their letters say Medicare uses the 4% rule, not the 3% one. 10 For patients on other insurance, the letters suggest scoring both ways and listing both AHIs. That way the same study still works once the patient joins Medicare.

If you live in Ohio, Michigan, Indiana or Kentucky, your CPAP claim goes to one of those two contractors. CGS handles Jurisdiction B, which covers all four states along with Illinois, Minnesota and Wisconsin. 12

Private plans vary. A 2022 review by the American Association of Sleep Technologists listed plans that wanted the 4% rule, including Aetna, all Medicare Advantage plans and some UnitedHealthcare dual plans. 11 The authors said the list was not complete and that plans can change their rules at any time. Call your plan and ask which rule it uses.

## Home Tests and the Missing Half of the 3% Rule

A wake up is seen on brain wave sensors, and most home tests don’t have them. So a home test can’t score the wake up half of the 3% rule. The AASM says that when a person at risk gets a negative home test, they should get a full overnight study in a lab. 2

That matters for the people the 4% rule already misses. A younger, leaner person whose shallow breaths end in wake ups can show few oxygen drops. A home test may score them low on either rule. Our guide to [choosing a home test or a lab study](https://nightwells.com/learn/home-test-or-lab/) covers who is better off in a lab.

Where a number is ours, the sentence says what it was measured on. Across Ohio, Michigan, Indiana and Kentucky, Nightwell lists 975 places under an overnight study in a lab, counted on our state pages as built on October 21, 2026. You can [find one by state](https://nightwells.com/providers/), then call and ask which rule it scores by.

*Image. A man asleep on his back wearing sleep study sensors on his face and scalp, a nasal tube and two chest belts*

A full sleep study setup. The small pads on the scalp read brain waves, which is how a lab sees the brief wake ups the 3% rule counts. Photo by [Clinique Somnomed](https://commons.wikimedia.org/wiki/File:Polysomnography_model.jpg), [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/).

## Read Your Own Report

Look for a line on how hypopneas were scored. It may say 3% or 4%, rule 1A or 1B, or name an AHI 3 and an AHI 4. Some reports give an RDI too, which adds other breathing events that end in a wake up. 2 Then match what you see to a row below and bring the question to your doctor.

| What your report shows | What it can mean | Ask your doctor or lab |
|---|---|---|
| One AHI and no rule named | You can’t compare it with another test or a plan rule | Which rule scored my hypopneas? |
| AHI under 5 on the 4% rule, and you still feel tired | The 3% count may be higher | Can you give me the 3% count or an RDI from the same night? |
| AHI 5 to 14 on the 4% rule, with Medicare | Medicare needs listed symptoms or conditions in your record | Are my sleepiness, blood pressure or other conditions written down? |
| AHI 15 or more on the 4% rule | You meet Medicare’s number for a CPAP trial | What is the next step and who supplies the machine? |
| Negative home test, still sleepy | The home device could not score wake ups | Should I have a full study in a lab? |

Comparing two tests? Only compare scores made with the same rule. A jump from 6 to 12 can be a change in the rule, not a change in you.

## Myths to Drop

### A higher 3% score means the lab padded it

The 3% rule is the rule the AASM recommends.

The higher number comes from counting breaths that end in a wake up, which the AASM says cause real sleepiness and harm. 2

### An AHI under 5 always means you’re fine

Under which rule? In the Swiss data, the AHI linked with high blood pressure was 10.7 on the 3% rule and 4.8 on the 4% rule. 3 The same health risk showed up at very different numbers, so a low score on the strict rule is not the whole story.

### Your AHI is your AHI

It’s a count made by a person and a rule book. Change the rule and the count changes. The Australian team found large gaps that differed from one patient to the next. 4

We’d rather you walk into your next visit with the right question than leave with the wrong number. Ask which rule was used, ask for both counts when your plan needs the 4% rule, and keep a copy of the full report.

## Handpicked

- [Home sleep test or a night in the lab](https://nightwells.com/learn/home-test-or-lab/)
- [What to expect at a sleep study](https://nightwells.com/blog/what-to-expect-at-a-sleep-study/)
- [Does insurance cover a sleep study?](https://nightwells.com/blog/does-insurance-cover-a-sleep-study/)
- [The 4 hour rule for CPAP](https://nightwells.com/blog/cpap-4-hour-rule/)
- [Sleep apnea providers by state](https://nightwells.com/providers/)

[Follow NightWells in Google Search](https://www.google.com/preferences/source?q=nightwells.com) to see more of our sleep apnea posts in your Top Stories.

## Public Records Used

1. [Skolnik and Attarian, The ethics of hypopnea scoring, Journal of Clinical Sleep Medicine, 2024 (PMC)](https://pmc.ncbi.nlm.nih.gov/articles/PMC10985313/). Opened October 2026.
2. [Malhotra and others, Polysomnography for obstructive sleep apnea should include arousal based scoring, AASM position statement, 2018 (PubMed)](https://pubmed.ncbi.nlm.nih.gov/29991439/). Opened October 2026.
3. [Hirotsu and others, Effect of three hypopnea scoring criteria on OSA prevalence, HypnoLaus, 2019 (PubMed)](https://pubmed.ncbi.nlm.nih.gov/30736872/). Opened October 2026.
4. [Ruehland and others, The new AASM criteria for scoring hypopneas, Sleep, 2009 (PubMed)](https://pubmed.ncbi.nlm.nih.gov/19238801/). Opened October 2026.
5. [Myllymaa and others, Effect of different oxygen desaturation threshold levels on hypopnea scoring, Sleep and Breathing, 2015 (PubMed)](https://pubmed.ncbi.nlm.nih.gov/25604477/). Opened October 2026.
6. [Tu and others, Comparing outcomes between 4% and 3% hypopnea scoring rules, Mayo Clinic, Sleep Medicine, 2024 (PubMed)](https://pubmed.ncbi.nlm.nih.gov/39395262/). Opened October 2026.
7. [Haile and others, Using expanded diagnostic criteria mitigates gender disparities, Journal of Clinical Sleep Medicine, 2025 (PubMed)](https://pubmed.ncbi.nlm.nih.gov/39565028/). Opened October 2026.
8. [CMS, National Coverage Determination 240.4, CPAP therapy for obstructive sleep apnea](https://www.cms.gov/medicare-coverage-database/view/ncd.aspx?NCDId=226). Opened October 2026.
9. [AbbasiMoradi and others, Age related disparities in sleep apnea diagnosis using a wearable device, Sleep Medicine, 2024 (PubMed)](https://pubmed.ncbi.nlm.nih.gov/38631159/). Opened October 2026.
10. [AASM, Medicare Administrative Contractors clarify sleep study scoring requirements, 2019](https://aasm.org/medicare-sleep-study-scoring-requirements/). Opened October 2026.
11. [AAST, Compliance Corner, Review of commercial treatment medical policy for obstructive sleep apnea, 2022](https://aastweb.org/compliance-corner-review-of-commercial-treatment-medical-policy-for-obstructive-sleep-apnea/). Opened October 2026.
12. [CGS Medicare, Jurisdiction B DME MAC](https://www.cgsmedicare.com/jb/index.html). Opened October 2026.

NightWells publishes information, not medical advice. Nothing here replaces being seen by a clinician who can examine you.

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Source page: https://nightwells.com/blog/3-percent-vs-4-percent-rule-sleep-apnea/