The BOLT score (Body Oxygen Level Test) is the single most useful metric for assessing your everyday breathing efficiency. Developed by Patrick McKeown and rooted in the Buteyko breathing method, it measures your body's tolerance to carbon dioxide — the primary driver of your urge to breathe. Unlike a maximum breath hold (which tests willpower), the BOLT score captures the moment your body first signals a need to breathe after a normal exhale, making it a reliable indicator of your baseline CO2 setpoint and habitual breathing volume.
Most adults score between 15 and 25 seconds on the BOLT test, well below the 40-second target that McKeown identifies with optimal breathing. A low BOLT score is strongly correlated with chronic over-breathing (hyperventilation), which has cascading effects on health: it depletes CO2 below the level needed for efficient oxygen delivery (the Bohr effect), constricts cerebral and peripheral blood vessels, shifts blood pH toward alkalosis, and maintains chronic low-grade sympathetic nervous system activation. This explains why people who over-breathe often experience anxiety, poor sleep, brain fog, and exercise intolerance — even when their blood oxygen saturation reads a normal 97 to 99 percent.
The Buteyko method, on which the BOLT score is based, was developed by Dr. Konstantin Buteyko in the 1950s and has since accumulated substantial clinical evidence, particularly for asthma. A 2008 Cochrane review found that Buteyko breathing reduced bronchodilator use by 90% in asthma patients. The core principle is simple: breathe less. By practicing nasal breathing, reduced volume breathing, and light breath holds throughout the day, you gradually raise your CO2 setpoint, and your BOLT score increases accordingly.
This free test walks you through the BOLT protocol step by step, times your hold automatically, and provides a personalized interpretation of your score with specific recommendations for improvement. Test yourself first thing in the morning for the most consistent results.
Read the physiology behind the number in our guide to CO2 tolerance, or the deeper background on what a BOLT score predicts. Athletes have the most to gain here: a higher score raises the intensity you can hold before breathing turns urgent, which is why breathwork for athletes starts with BOLT rather than with lung capacity. Pair the test with the breathing rate calculator to see both halves of your breathing pattern.
