What Is Vagal Tone and How to Measure It

Vagal tone is a measure of how well your vagus nerve is working. It reflects how quickly your body can shift out of stress and back into calm. Higher vagal tone is linked to better sleep, steadier mood, smoother digestion, and faster recovery from stress. You can measure it indirectly with heart-rate variability (HRV) and with a CO2 tolerance breath test, and the best part is that it is trainable.

What is vagal tone, exactly?

The vagus nerve is the longest nerve of your autonomic nervous system and the main driver of the parasympathetic, or "rest and digest," branch. It runs from your brainstem down through your throat, heart, lungs, and gut. Vagal tone describes the strength and responsiveness of that nerve, in other words, how readily it applies the brake when your body needs to calm down.

Think of it like cardiovascular fitness, but for your nervous system. A person with high vagal tone calms down quickly after a stressor and returns to a relaxed baseline. A person with low vagal tone stays revved up, takes longer to settle, and feels the effects of stress more sharply.

This is the whole idea behind The Vagal Method. You don't find calm, you return to it. And the faster you return, the more unshakeable you become. Vagal tone is simply the measure of how fast you come back.

Why vagal tone matters

Your vagus nerve touches almost every system involved in how you feel day to day. When vagal tone is high, those systems run more smoothly. The benefits show up across the board:

• Stress recovery. You return to calm faster after a hard moment instead of staying on edge.
• Sleep. A stronger parasympathetic brake helps you fall asleep and stay asleep.
• Mood and resilience. Higher vagal tone is associated with steadier mood and better emotional regulation.
• Digestion. The vagus nerve runs the gut, so good tone supports smoother digestion.
• Heart health. Vagal activity is closely tied to heart-rate variability, a marker of cardiovascular and autonomic health.

Low vagal tone tends to do the opposite. If several of those areas feel off, it can be a sign of a dysregulated nervous system, which is often a vagal-tone problem at its root.

How to measure vagal tone

You cannot put a sensor directly on the vagus nerve, so vagal tone is measured through proxies. The two most practical are HRV and CO2 tolerance.

Heart-rate variability (HRV)

HRV is the variation in time between your heartbeats. A healthy heart does not beat like a metronome. It speeds up slightly on the inhale and slows on the exhale, and that flexibility is driven largely by the vagus nerve. Higher HRV generally means higher vagal tone. You can track it with most fitness wearables and rings, ideally first thing in the morning for a consistent reading.

CO2 tolerance

CO2 tolerance reflects how comfortably your body handles a rise in carbon dioxide, which is closely linked to how calm and regulated your breathing system is. A higher tolerance points to a calmer, better-regulated nervous system and stronger vagal tone. The advantage of CO2 tolerance is that you do not need a wearable to measure it, just your breath and a timer.

The free Vagal Tone Breath Test uses exactly this method. It gives you a baseline score in about three minutes, so you can retest over time and watch your vagal tone climb as you train.

Can you improve your vagal tone?

Yes. Vagal tone responds to training the same way a muscle does. Slow breathing with long exhales, deliberate cold exposure, heat, humming, daily movement, and quality sleep all push it higher over time. A single session can calm you in minutes. Lasting change in your baseline usually shows up over two to six weeks of consistent daily practice. For the full toolkit, see how to increase vagal tone.

Where to start

Measure first, then train. Take your baseline with the breath test, then add two minutes of slow breathing with long exhales every morning. From there, layer in a cold finish to your shower and a minute of humming. That sequence of breath, heat, and cold is the foundation of the Vagal Method, built to train the one nerve that runs your stress, sleep, focus, and mood.