Heart Rate Variability (HRV) Resonance Finder

Current estimate

{{ cycle_seconds.toFixed(2) }} s / cycle · {{ summaryPattern }}

{{ resonanceBandBadge }} {{ window_low.toFixed(2) }}-{{ window_high.toFixed(2) }} bpm window {{ sexLabel }} RHR {{ rhr_bpm }} bpm Warnings: {{ warnings.length }}

Age:

Enter whole years, such as 35; values must be 1 or higher.

years

Height:

Enter standing height and choose cm or in; the tool converts to centimeters.

Sex:

Options: Male, Female, or Other / Prefer not to say.

Resting heart rate:

Use a calm seated reading in bpm, such as 60.

bpm

Exhale bias: {{ exhale_bias_percent }}%

Use -40% to 40%; 0% keeps inhale and exhale evenly split.

Hold after inhale:

Enter seconds; use 0 for no top hold.

Hold after exhale:

Enter seconds; use 0 for continuous breathing.

Vagal tone z-score:

Use -3 to 3; leave 0 when you do not track this proxy.

Fitness z-score:

Use -3 to 3; leave 0 for a neutral fitness adjustment.

Curve width add-on:

Use 0 to 1 bpm; 0 keeps the default response curve.

bpm

Round phase durations:

Turn on to show inhale, exhale, and hold durations to the nearest 0.1 s.

Metric	Value	Copy
{{ row.label }}	{{ row.value }}

Trial	Rate	Cycle	Inhale	Hold in	Exhale	Hold out	Copy
{{ row.label }}	{{ row.rateLabel }}	{{ row.cycleLabel }}	{{ row.inhaleLabel }}	{{ row.holdInLabel }}	{{ row.exhaleLabel }}	{{ row.holdOutLabel }}

Area	Value	Detail
Start window	{{ window_low.toFixed(2) }}-{{ window_high.toFixed(2) }} bpm	Use the window as a comfort-first starting range, then refine with direct HRV feedback when available.
Breath shape	{{ summaryPattern }}	Keep the pattern smooth. Reduce holds or exhale bias if the pace feels forced.
Use boundary	Estimator only	This is not a medical device. Stop if you feel dizzy, strained, or unwell.

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Heart rate variability, or HRV, changes with breathing. During slow paced breathing, heart rate often rises during inhale and falls during exhale. HRV resonance practice looks for a breathing rate that makes that rhythm especially strong, commonly as part of biofeedback or slow-breath training.

A true resonance frequency is usually found by testing several nearby breathing rates while measuring heart rate and respiration. This estimator does not measure HRV directly. It gives a starting pace from age, height, sex, resting heart rate, and optional proxy fields, then turns that pace into a breath-cycle map, phase timings, nearby trial steps, and a response curve.

Estimated resonance center rate with a nearby trial window on a response curve

The output should be read as a practice plan, not a diagnosis or lab result. The breathing rate tells you where to start, the window suggests nearby rates to try, and the response curve shows how the model is centered. Comfort matters more than the second decimal place; slow breathing that causes strain, dizziness, or air hunger should be softened or stopped.

The most useful first pass is often simple: enter calm resting values, keep advanced fields neutral, try the center rate briefly, and then explore nearby rates only if the rhythm feels smooth.

How to Use This Tool:

Use ordinary resting values first. Advanced adjustments are better for refinement after the neutral result makes sense.

Enter Age, Height, Sex, and Resting heart rate. Use a calm seated pulse rather than a recent exercise reading.
Read the summary Current estimate, cycle length, and pattern. These translate the rate into seconds per breathing cycle.
Use the breath-cycle band below the summary to check how inhale, exhale, and any holds divide one full cycle before adjusting fields.
Check Breathing Metrics for Resonant rate (bpm), Cycle length (s), inhale, exhale, hold values, Recommended window (bpm), and Status.
Open Trial Ladder when you want practical nearby paces to test. It shows slower and faster probes, the window endpoints, and the center estimate using the same phase settings.
Open Advanced only when you want to reshape the breath. Exhale bias changes the inhale/exhale split, hold fields insert pauses, and Round phase durations makes displayed timings easier to count.
Use Vagal tone z-score, Fitness z-score, and Curve width add-on cautiously. Leave them at zero when you do not have a clear reason to nudge the estimate.
Open Resonance Profile to compare the center rate with the nearby trial window. Treat the curve as a model, not as a measured HRV response.
If an error says holds leave no time for inhale or exhale, reduce the hold durations or use a faster center before trying the rhythm.

Interpreting Results:

Resonant rate (bpm) is the center estimate. It is the starting breathing frequency after the entered values and proxy adjustments are applied. It is not proof of a person's measured resonance frequency.

Cycle length (s) is often the easiest number to follow. It is 60 divided by the center rate. The inhale, exhale, and hold rows then show how that full cycle is divided into a pattern you can count.

Recommended window (bpm) is a trial band around the center. A nearby rate can feel smoother even when the center estimate looks mathematically tidy. Use the window for small experiments, especially when direct HRV feedback is not available.

Trial Ladder converts that idea into rows you can test: a slower probe, the lower window edge, the center estimate, the upper window edge, and a faster probe. The phase timings in those rows keep the same hold and exhale-bias settings so the only major difference is rate.

Status and warnings are practical safeguards. Errors block invalid patterns, such as holds that consume the full cycle. Warnings flag values that still calculate but deserve caution, including unusual resting pulse, large exhale bias, or an estimated rate outside the common adult slow-breath range.

The main false-confidence risk is treating the curve peak as a measurement. The chart is normalized so the modeled center peaks at 1.0. It does not mean your HRV response was measured or optimized.

Technical Details:

Published HRV resonance assessment protocols commonly test adults at slow paced rates such as 6.5 down to 4.5 breaths per minute while monitoring heart-rate oscillation and respiration. The goal is to find the breathing rate that best stimulates the baroreflex and maximizes respiratory sinus arrhythmia for that person. This page uses a transparent heuristic instead of a sensor-based assessment.

The estimator starts at 5.5 breaths per minute, then applies small shifts for broad age bands, height relative to 170 cm, sex selection, resting heart rate relative to 60 bpm, and optional proxy values. The final center is rounded to two decimals and clamped to 4 to 8 bpm. The displayed band label treats values below 4.8 bpm as slow, values above 6.6 bpm as fast, and the range between them as the common band.

Formula Core

The center estimate is a deterministic score from the visible inputs. Heights entered in inches are first converted to centimeters.

\begin{array}{lcl} dHeight & = & clamp (- 0.4, 0.4, - 0.4 \times \frac{heightCm - 170}{100}) \\ dRHR & = & clamp (- 0.5, 0.5, \frac{rhr - 60}{40} \times 0.35) \\ centerBpm & = & clamp (4, 8, round2 (5.5 + dAge + dHeight + dSex + dRHR - 0.12 vagalZ - 0.08 fitnessZ)) \\ cycleSeconds & = & \frac{60}{centerBpm} \end{array}

HRV resonance center adjustment rules
Adjustment	Rule	Effect
`dAge`	Age <=20: +0.25; <=35: +0.10; <=50: 0; <=65: -0.15; <=80: -0.30; above 80: -0.45.	Younger entries trend faster; older entries trend slower.
`dSex`	Male: 0; female: +0.08; other or prefer not to say: +0.04.	Small fixed offset only.
`vagalZ` and `fitnessZ`	Subtract 0.12 bpm per vagal z unit and 0.08 bpm per fitness z unit.	Positive proxy values slow the center slightly.

Once the center rate is known, the breath pattern is built from the cycle time. Holds are removed first. The remaining time is split between inhale and exhale according to the exhale-bias percentage.

\begin{array}{lcl} available & = & cycleSeconds - holdIn - holdOut \\ exhaleFraction & = & clamp (0, 1, 0.5 + \frac{exhaleBiasPercent}{200}) \\ inhaleSeconds & = & available \times (1 - exhaleFraction) \\ exhaleSeconds & = & available \times exhaleFraction \end{array}

The trial window width starts at 0.35 bpm, narrows or widens with the optional proxy fields, accepts the manual width add-on, and is clamped between 0.15 and 0.8 bpm. The displayed low and high window endpoints are each clamped to 3 to 9 bpm. The trial ladder also adds probes 0.5 bpm below and above the center estimate, clamped to the same 3 to 9 bpm display range.

\begin{array}{lcl} width & = & clamp (0.15, 0.8, 0.35 \times clamp (0.7, 1.4, 1 - 0.08 vagalZ - 0.04 fitnessZ) + widthAdd) \\ windowLow & = & clamp (3, 9, centerBpm - width) \\ windowHigh & = & clamp (3, 9, centerBpm + width) \end{array}

The response curve is a normalized bell-shaped curve across 3 to 9 bpm. Its peak is set at the center estimate, and its spread is derived from the window width. It supports comparison of nearby trial rates, not measurement of physiological response.

Responsible Use Note:

This is an informational pacing estimator, not a medical device, diagnostic test, or substitute for supervised HRV biofeedback. People with breathing, cardiovascular, pregnancy-related, panic, fainting, or medical concerns should use professional guidance before slow-breath training.

Stop or soften the pace if you feel dizzy, strained, short of breath, or unwell.
Remove holds before changing the center rate when the pattern feels forced.
Do not use the exact decimal output as proof of a measured personal resonance frequency.
Changed values can be reflected in the page URL, so avoid sharing links when health or body data should stay private.

Worked Examples:

Neutral adult starting point

With age 35, height 170 cm, sex set to Other, and resting heart rate 60 bpm, the center estimate is 5.64 bpm. Cycle length (s) is about 10.64, and with no holds or exhale bias, inhale and exhale split the cycle evenly. The trial ladder adds slower and faster rows so you can compare nearby paces without recalculating them by hand.

Longer exhale without changing the center

Starting from the same neutral case, set Exhale bias to 20% and Hold after exhale to 1.0 s. The Resonant rate (bpm) stays 5.64, but the pattern shifts toward a longer exhale and a short bottom hold.

Hold timing error

At a slow center rate, entering large values for both hold fields can leave no time for inhale or exhale. The page shows an error instead of a breathing pattern. Reduce Hold after inhale (s) or Hold after exhale (s), then check Status again.

FAQ:

Does this measure my HRV?

No. It estimates a starting breathing rate from entered values and draws a model curve. It does not read a heart sensor, respiration belt, or live HRV stream.

Is the exact rate my true resonance frequency?

No. Treat it as a first target to test. True HRV resonance is normally identified by comparing several paced breathing rates with heart-rate and respiration feedback.

Why does exhale bias not change the center rate?

Exhale bias changes how the cycle time is divided between inhale and exhale. The center rate still comes from the estimator inputs, so the full cycle length stays tied to the same bpm value.

What does the curve-width add-on do?

It widens the suggested trial window and the plotted curve spread. It does not move the center rate.

Why did I get a warning instead of an error?

A warning means the page can still calculate, but one input deserves caution. Examples include a resting heart rate outside common resting ranges or a large exhale bias.

What should I do if slow breathing feels uncomfortable?

Stop, remove holds, reduce the exhale bias, or try a gentler nearby pace. A useful breathing rhythm should feel repeatable without strain or dizziness.

Glossary:

HRV: Heart rate variability, the variation in time between heartbeats.
Resonance frequency: The breathing rate that best amplifies breathing-linked heart-rate oscillation for a person during assessed practice.
Baroreflex: A blood-pressure regulation loop that helps adjust heart rate and vessel tone.
Respiratory sinus arrhythmia: The normal pattern where heart rate tends to rise during inhale and fall during exhale.
Exhale bias: The setting that shifts more or less of the available cycle time into exhale.
Recommended window: The trial band around the estimated center breathing rate.

References:

A Practical Guide to Resonance Frequency Assessment for Heart Rate Variability Biofeedback, Frontiers in Neuroscience, 2020.
The Impact of Resonance Frequency Breathing on Measures of Heart Rate Variability, Blood Pressure, and Mood, Frontiers in Public Health, 2017.
Controlled Breathing Exercise, NHS inform, December 9, 2025.