Understanding Your CPAP Data: What the Numbers Actually Mean
Understanding Your CPAP Data: What the Numbers Actually Mean
Your machine hands you an AHI, a leak rate, and a score out of 100 — and nobody explains what any of it means. Here's the plain-English version.
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Most CPAP guides tell you how to fix a leak or clean your mask. Almost none explain what you're actually looking at every morning when your app shows you a score, a percentage, and a string of numbers you were never given a key for.
That gap causes two opposite problems: people who ignore genuinely concerning data because it looks fine at a glance, and people who panic over normal, expected fluctuation. This guide is the missing key — what AHI, leak rate, usage hours, and your overall score actually represent, and what's worth acting on.
The single most important number on your report.
AHI stands for Apnoea-Hypopnoea Index — the average number of breathing interruption events per hour of sleep.
These bands are commonly cited clinical reference ranges for untreated OSA severity — but on CPAP, the goal is usually to bring your AHI down into the normal range, and your clinician may set a different personal target based on your original sleep study. A single high night usually isn't meaningful on its own; a rising trend across several weeks is what's worth flagging.
The number that quietly undermines everything else.
Leak rate measures how much air is escaping around your mask rather than reaching your airway as intended — usually shown in litres per minute, or as a simple percentage or colour flag depending on your app.
A small amount of "intentional" leak through your mask's vent holes is normal and by design — CPAP masks are built to vent exhaled air. What matters is unintentional leak: air escaping from a poor seal around your face. This is usually what your app is actually flagging when it shows a leak warning.
A consistently high or frequently flagged leak rate can quietly reduce how effectively your prescribed pressure reaches your airway — sometimes enough to keep your AHI artificially low-looking while comfort and therapy quality both suffer. If your leak rate is regularly flagged, it's worth working through mask fit before assuming everything is fine just because your AHI looks acceptable.
"Compliant" isn't the same as "optimal."
Many insurers and clinics use a minimum compliance threshold — commonly around 4 hours a night on at least 70% of nights — as a baseline for demonstrating regular use. This threshold exists mainly for monitoring and funding purposes, not because 4 hours is the ideal amount of therapy.
Using CPAP for your entire sleep period gives the greatest benefit. If your usage hours consistently sit right at the compliance minimum, there's usually room to get meaningfully more out of your therapy by simply wearing it longer each night, not by changing anything else.
The single number is a summary, not the full picture.
ResMed's myAir app rolls several factors into one score out of 100 each morning. In general terms, it reflects a combination of:
ResMed doesn't publish the exact weighting of the formula, so treat the overall score as a quick daily snapshot rather than a precise clinical measure. If your score is lower than expected, the more useful step is opening the detail view and checking which individual component dropped — usage, seal, or events — rather than fixating on the headline number.
OSCAR software: more detail, if you want it.
OSCAR (Open Source CPAP Analysis Reporter) is a free, independent program that reads the detailed data most CPAP machines record to an SD card, and displays it as night-by-night charts — far more granular than the summary view in apps like myAir.
It isn't necessary for everyone, and it won't replace advice from your sleep clinic. But for users who want to see exactly when events occurred during the night, correlate them with sleeping position, or track trends over months, it's a genuinely useful free tool that many long-term CPAP users in the UK and internationally rely on alongside their manufacturer app.
Good, watch, or act — a rough guide.
Not a diagnosis — a starting point for deciding whether to keep going, keep an eye on things, or get in touch with your clinic.
- AHI consistently under 5
- Leak rate rarely flagged
- Usage covering most of your sleep period
- AHI occasionally spikes on individual nights
- Leak rate flagged a few nights a week
- Usage hovering right at the compliance minimum
- AHI trending upward over several weeks
- Leak rate flagged most nights despite refitting
- Usage dropping well below compliance minimums
Quick answers to common questions.
What is a good AHI on CPAP?
What counts as a high leak rate on CPAP?
How many hours a night should I use CPAP?
Why is my myAir score low even though I feel fine?
What is OSCAR software and do I need it?
More CPAP guides on this site.
Your CPAP data isn't there to grade you — it's there to help you and your clinician spot patterns early. A single rough night rarely means much on its own. What matters is the trend across weeks: AHI drifting up, leak rate staying stubbornly flagged, or usage hours quietly slipping.
Check your numbers the way you'd check a weather forecast — useful context for the days ahead, not a verdict on any one night. If a trend genuinely concerns you, that data is exactly what your sleep clinic needs to help.
This guide is for general educational purposes only and does not replace personalised medical advice. AHI severity bands and compliance thresholds reflect commonly cited general reference ranges — your own targets should be set by your prescribing clinician or sleep clinic based on your individual diagnosis.
Never adjust your prescribed pressure settings based on this guide alone. If you have concerns about your therapy data, contact your GP, sleep clinic, or CPAP provider.