Free Health & Breathing Calculators
Free interactive calculators for the metrics that matter — HRV, sleep, heart-rate zones, caffeine timing, protein and more. Every tool reads your number against the published evidence, not a round-number rule of thumb, and tells you what actually moves it.
No sign-up, no account, nothing to install — they run right in your browser. When you want your resting pulse, HRV and breathing rate tracked automatically over time instead of typed in once, that’s what ONDA Life does on your iPhone and Apple Watch.
Camera-based pulse, breathing and nervous-system readout — your body, in real time, right in the browser.
Enter your age, sex and morning RMSSD (Oura, Whoop, Garmin, Polar, Fitbit) to compare it with about 8 million Fitbit users your age — a comparison, not a medical norm.
Find the latest you can have your last coffee before bed without leaving sleep-disrupting caffeine in your system.
Add up your last 7 nights to see your accumulated sleep deficit against your age-based need — and how to repay it.
Find your aerobic-base (Zone 2) heart rate and all 5 training zones from your age — using the accurate Tanaka formula.
Six questions to find your body-clock type — morning, intermediate or evening — with a personalised daily-timing protocol.
Get your daily protein target in grams from your bodyweight and goal — based on ISSN/ACSM guidelines — plus a per-meal split.
Estimate your cardiorespiratory fitness from your resting and max heart rate, and see where it ranks against age- and sex-based norms.
Find your total daily calorie burn with the Mifflin–St Jeor equation, plus a calorie target and macro split for your goal.
Estimate your daily water target from bodyweight, with adjustments for exercise, hot weather and high caffeine or alcohol intake.
Add your drinks, weight and sex to estimate blood alcohol (‰ and %) and how many hours until it is back to zero.
Pick a protocol (16:8, 18:6, 20:4, OMAD) and first-meal time to get your eating and fasting windows, plus a metabolic-phase timeline.
Enter your trip to see which way your body clock must shift and exactly when to seek and avoid bright light to beat jet lag faster.
Estimate your 1RM from a hard set with the Epley and Brzycki equations, plus a training-load table for every percentage of your max.
Estimate your body-fat percentage with just a tape measure using the U.S. Navy circumference method, and see your fitness band.
Find the best bedtime or wake time by aligning your alarm with ~90-minute sleep cycles, so you wake in lighter sleep and less groggy.
A drug-free way to fall asleep faster: picture a stream of random neutral words (serial diverse imagining) to crowd out bedtime worry-loops.
Guided breathing with an animated circle and sound cues: box breathing, 4-7-8, coherent breathing, extended exhale and the physiological sigh.
Find the slow breathing rate (about 4.5–7/min) where your HRV peaks — your personal resonance frequency — with a height estimate and a paced circle.
Build a structured "dopamine detox" — really stimulus control — to cut the cheap-reward loops hijacking your focus and rebuild drive for what matters.
Estimate your VO2max with the published HUNT model and see your fitness age — the age of an average healthy person as fit as you.
Build a realistic screen-reset plan — evidence-based swaps and a phone-setup checklist to reclaim your attention and sleep, without a purity test.
An 8-question stress-load check across exhaustion, detachment and efficacy — with a recovery-focused next step. Educational, not a diagnosis.
Are you in fight-or-flight, shutdown or regulated? Read your current autonomic state and get the right vagal-tone protocol to shift it.
A guided Wim Hof breathing timer plus a safety-first cold-exposure protocol — stress-resilience training, honestly framed with the real risks.
Pinpoint which factors — sleep, stress, overstimulation or lifestyle — are clouding your focus, with a targeted fix and tools for each.
Enter your age, sex and resting pulse to see your percentile against CDC norms for men and women — plus what lowers it.
What Whoop, Oura and Garmin recovery scores really measure (HRV, resting HR, sleep) — plus a quick readiness estimate and what to do today.
Measure your pulse with just your phone camera — fingertip on the lens, heartbeat in real time. A live taste of how ONDA reads your body, no wearable needed.
Measure your breathing rate with your phone mic and slow toward the ~6 breaths/min calm zone — live breath biofeedback, no wearable needed.
Breathe with the pacer while your phone camera reads your pulse — watch your heart rate rise on the inhale and fall on the exhale. ONDA in miniature.
See what your Apple Watch already recorded — two weeks of resting pulse, HRV and breathing read from your own Health data, on your iPhone. The range, not one number. Nothing is uploaded.
A free interactive feelings wheel. Name what you feel right now, then take a quiet moment to be with it — no sign-up, no diagnosis, no advice.
About these tools
These are the small, focused calculators the quantified-self and biohacking world keeps reaching for — heart-rate variability, sleep debt, caffeine half-life, training zones, protein needs — collected in one place and, where it matters, tied to the science rather than left as a bare number. The point isn’t the number itself; it’s reading it in context: what’s normal for your age, what a change actually signals, and which lever moves it.
Wherever a tool touches your nervous system — HRV, resting heart rate, stress load — it links through to what ONDA measures and the evidence behind it, so you can see the caveats, not just the output. We’d rather a calculator make you a little more skeptical and a little better informed than hand you a false-precision score.
Nervous system & recovery14 tools
Heart-rate variability, resting heart rate and stress-load calculators that read your autonomic state — the balance between the “fight-or-flight” sympathetic branch and the “rest-and-digest” parasympathetic one. These are the metrics ONDA Life is built around, so each one links back to what the number actually means and what reliably moves it.
Sleep6 tools
Sleep-debt, caffeine cut-off and chronotype tools that turn sleep from a vague target into concrete timing. Sleep is the single biggest lever on next-day HRV and recovery, so getting the timing of caffeine, light and bedtime right pays back everywhere else.
Fitness & training4 tools
Heart-rate-zone and training-load calculators — including a Zone 2 aerobic-base estimate from the accurate Tanaka age formula — so you can train at the intensity you actually intend rather than guessing.
Nutrition4 tools
Protein, hydration and intake calculators grounded in published guidelines (ISSN/ACSM), giving you a defensible daily target and per-meal split instead of a round-number rule of thumb.
Focus, dopamine & longevity4 tools
Attention, reward-balance and healthspan tools for the longer game — the habits and rhythms that compound over months, not the metric you check each morning.
How to read your numbers honestly
A single reading is a snapshot, and snapshots are noisy — HRV alone swings with sleep, hydration, alcohol, illness and even how you sat down. Your own trend over days and weeks is far more meaningful than one figure, and comparing your absolute number to someone else’s is rarely useful. These tools are for orientation and self-experiment, not diagnosis; they don’t replace a clinician. Used that way, they’re a fast, honest way to turn a metric you’ve heard about into something you can actually act on.
Want the nervous-system side tracked continuously instead of typed in? See what ONDA Life does, or how it compares to the wearables and apps people cross-shop.
Best Apps That Combine Breathing, HRV & Real-Time Feedback →