Target heart rate Karvonen calculator

This capability applies HR max equals two hundred twenty minus age, computes reserve, multiplies by intensity, and returns structured JSON with maximum HR, reserve, target bpm, and both percent and fraction forms of intensity. The path is pure arithmetic with no network and no random seed, so coaching apps, PE labs, and prepaid API clients get identical results every time. When resting heart rate meets or exceeds the estimated maximum, the request fails with invalid input because reserve cannot be zero or negative for a meaningful Karvonen target.

What the Karvonen reserve method measures and which inputs you need

Send required fields age, resting_hr, and intensity as finite numbers; aliases years and age_years work for age, resting, rhr, rest_hr, resting_heart_rate, and hr_rest work for resting rate, and intensity_percent, percent, pct, intensity_pct, and target_percent work for intensity. Identical inputs always yield identical JSON because the algorithm never touches the network, a model, a clock, or a random generator. Missing fields, non-finite values, out-of-range age or intensity, and resting rates that meet or exceed estimated maximum all fail with invalid_input and are not charged.

Reading the response fields and interpreting target heart rate

Remember that two hundred twenty minus age is only an estimate—true maximum varies with genetics, medication, and sport, and this calculator does not accept a custom measured maximum. On success the response echoes age and resting_hr, then intensity_percent and intensity_fraction so UIs can show either form without recomputing. The field hr_max is estimated maximum heart rate as two hundred twenty minus age, hrr is heart-rate reserve as hr_max minus resting_hr, and target_hr is the Karvonen target in beats per minute: resting plus intensity times reserve. The unit field is always bpm, formula restates the reserve equation, and method is always karvonen_reserve so downstream code can branch without sniffing shapes. Use target_hr for a single training number on a watch or console; use hr_max and hrr when you want to show the intermediate steps students learn on paper; use intensity_fraction when chaining zone logic that already works on zero-to-one scales. Resting heart rate that equals or exceeds estimated maximum is impossible for a positive reserve and raises a clear invalid_input message that mentions resting rate exceeding maximum. Do not confuse this endpoint with pure percentage-of-max formulas that ignore resting rate, with lactate-threshold zones, or with clinical stress-test targets: those are different intents.

API usage, pricing, coaching workflows, and practical limits

Call the free in-browser target heart rate Karvonen calculator for PE classes, gym floor demos, and quick client checks without rebuilding the reserve arithmetic in every spreadsheet. Prefer consistent morning resting measurements; if your UI collects intensity only as whole percents, send seventy rather than zero point seven—the engine accepts both. Keep expectations educational: this is a planning and learning tool, not a diagnostic medical device, and people with cardiac conditions, medications that alter heart rate, or physician restrictions should follow professional advice rather than any single formula alone. Send a JSON body with required age, resting_hr in beats per minute, and intensity as a percent or fraction. Use the prepaid API when a coaching SaaS, wearable companion, school LMS, or training log needs a stable contract under KIT balance at $0.002 per successful item; validation failures never consume balance after the engine rejects the request. Pair this endpoint with your own resting-rate measurement workflow, then store target_hr alongside zone labels for warm-up, aerobic base, and tempo sessions. Authors shipping SDKs can map target_hr, hr_max, and hrr into dashboards and export CSV columns for age, resting rate, intensity, and Karvonen target—the same numbers coaches compute by hand after measuring a resting pulse.