Your CPAP machine records detailed data every night, and learning to read it gives you a clear picture of how well your therapy is working. The most important numbers to watch are your AHI (events per hour), usage hours, leak rate, and pressure. Most of this data is available through your machine’s built-in screen, a manufacturer app, or free third-party software.
The Key Metrics and What They Mean
Every modern CPAP machine tracks a core set of numbers. Here’s what each one tells you:
- AHI (Apnea-Hypopnea Index): The number of times per hour your breathing paused or became dangerously shallow. This is the single most important number on your report. Harvard Medical School classifies the severity scale like this: below 5 is normal, 5 to 14 is mild sleep apnea, 15 to 29 is moderate, and 30 or above is severe. Your goal on CPAP therapy is to keep this below 5.
- Usage hours: How long you actually wore your mask each night. Four hours is generally the minimum threshold for effective therapy, and it’s also the number insurers look at for compliance. Patients who actively engage with their data average around 5 to 6 hours per night.
- Leak rate: How much air escapes from your mask, measured in liters per minute (L/min). Some leakage is intentional, built into your mask’s exhaust port. What matters is unintentional leakage from a poor seal or your mouth falling open.
- Pressure: The air pressure your machine delivers, measured in centimeters of water pressure (cm H₂O). If you use an auto-adjusting machine, this number changes throughout the night based on what your airway needs.
Understanding Your AHI Score
Your residual AHI is the number of breathing events still occurring while you use CPAP. Think of it as your treatment scorecard. If your AHI before therapy was 35 (severe) and your residual AHI on CPAP is 2.7, your machine is eliminating the vast majority of events. That’s a sign therapy is working well.
If your residual AHI is consistently above 5, something needs attention. The machine might need a pressure adjustment, your mask might not be sealing properly, or you may need a different mask style. Some machines break AHI into subcategories: obstructive events (your airway physically collapses), central events (your brain temporarily stops sending the signal to breathe), and hypopneas (partial reductions in airflow). A high number of central events in particular is worth flagging to your sleep provider, since it can indicate a different type of sleep apnea that requires a different approach.
What Leak Rate Numbers Actually Mean
Leak data can be confusing because every mask has intentional leak built in. The number your machine reports may be total leak (intentional plus unintentional) or just unintentional leak, depending on your device and software. Check your machine’s documentation to know which one you’re seeing.
As a general benchmark, keeping unintentional leak below 24 L/min is considered good. Research published in the Journal of Clinical Sleep Medicine used 40 L/min of total leak as the dividing line between low and high leakage, with anything above that associated with reduced therapy quality. When leaks climb above roughly 52 to 70 L/min total, the machine may no longer be able to accurately detect breathing events or deliver the correct pressure. At that point, your AHI data for the night becomes unreliable too.
If you see high leak numbers, the most common causes are a mask that doesn’t fit your face shape, a worn-out cushion, or your mouth falling open during sleep (especially with a nasal mask). Chin straps or a full-face mask can help with mouth leaks.
Reading Pressure Data
If you use a fixed-pressure CPAP, your pressure is a single number set by your provider. There’s not much to interpret. But if you use an auto-adjusting machine (often called APAP), the pressure varies throughout the night, and your data report will show a range.
The number to pay attention to is the 90th or 95th percentile pressure. This tells you the pressure level your machine stayed at or below for 90% or 95% of the night. It’s a useful proxy for how much pressure your airway actually needs. If your machine is set to a range of 5 to 15 cm H₂O and your 95th percentile is 12, your airway needs close to 12 for most of the night. If that number creeps up over time, it could signal weight gain, increased congestion, or worsening apnea. If it sits at the very top of your machine’s range, your provider may need to raise the ceiling.
Conversely, if your 95th percentile pressure is low, say 7 or 8, and your AHI is well controlled, your therapy is working efficiently without needing to push much air.
Where to Find Your Data
There are three main ways to access CPAP data, and each gives you a different level of detail.
The Machine’s Built-In Screen
Most machines display a basic summary when you press the info button: last night’s AHI, usage hours, and sometimes leak rate. This is fine for a daily check-in but doesn’t show trends or detailed breakdowns. Some machines also have a clinician menu with more advanced settings. On ResMed devices, for example, you can access this by pressing and holding the dial and Home button simultaneously for three seconds.
Manufacturer Apps
ResMed’s myAir and Philips’ DreamMapper connect to your machine via Bluetooth or cellular and display your data on your phone. These apps typically show nightly AHI, usage hours, mask seal quality, and a simplified score. MyAir, for instance, gives you a daily score out of 100 based on usage time, mask seal, events per hour, and how many times you took the mask off. These apps are convenient and well-designed for daily tracking, but they simplify the data significantly. You won’t see breath-by-breath patterns or detailed pressure graphs.
OSCAR Software
For the most detailed view, OSCAR (Open Source CPAP Analysis Reporter) is free software that reads raw data from your machine’s SD card. It displays everything: AHI broken into event types, leak rate over time, pressure adjustments throughout the night, flow rate showing the shape of each individual breath, and usage hours. The flow rate chart is especially useful because it lets you see the pattern of your breathing in real time, revealing things like periodic breathing clusters or flow limitations that don’t quite register as scored events. OSCAR works with most ResMed and Philips machines, as well as some other brands. You just remove the SD card, plug it into your computer, and import the data.
Patterns Worth Watching Over Time
A single night of data isn’t very meaningful. What matters are trends over weeks and months. Here’s what to look for:
A gradually rising AHI could mean your mask is deteriorating, your weight has changed, or your pressure needs adjustment. If your AHI jumps suddenly on one night but is fine the rest of the week, it was likely caused by sleeping position, alcohol before bed, or nasal congestion. Don’t worry about isolated spikes.
Leak rates that climb over several weeks usually point to a mask cushion that needs replacing. Most silicone cushions lose their seal after one to three months of regular use. If your leak rate is high from the very first night with a new mask, the mask style or size is probably wrong for your face.
If you notice snoring data on your report (some machines track this), it typically means your pressure is too low to fully hold your airway open. This is worth mentioning at your next appointment.
A steady increase in your 95th percentile pressure over months, especially combined with rising AHI, suggests your airway obstruction is getting worse. Weight gain is the most common driver, but seasonal allergies and nasal issues can contribute too.
Insurance Compliance and Your Data
If your CPAP is covered by insurance, your usage data determines whether coverage continues. Medicare and most private insurers require you to use your machine for at least 4 hours per night on at least 70% of nights during a consecutive 30-day period within the first 90 days of therapy. Your provider checks this data at a follow-up visit, and the machine reports it automatically through cloud-connected platforms. If you fall short, your insurer can stop covering the equipment.
After that initial compliance window, annual check-ins with your sleep provider are still important. Even if your numbers look great, having a clinician review your detailed data can catch subtle issues you might miss on a nightly summary screen.