Heart rate zones from reserve

This heart rate zones from reserve calculator accepts required hr_rest and hr_max in beats per minute, subtracts rest from max to obtain reserve, then maps the classic fifty-to-sixty, sixty-to-seventy, seventy-to-eighty, eighty-to-ninety, and ninety-to-one-hundred percent bands onto that reserve and adds resting rate back so every bound is a real training pulse. The path is pure arithmetic with no network and no random seed, so homework checkers, training logs, and prepaid API clients receive identical JSON every time. Missing required fields, non-finite values, non-positive bpm, or a maximum that is not strictly above rest all fail with invalid_input and are not charged.

What the percent-reserve method measures and which inputs you need

Heart-rate reserve is the gap between the pulse you sit at and the pulse you can reach at a true maximum effort. The percent-reserve method, widely taught as the Karvonen-style percent-HRR layout, does not take a flat percentage of maximum heart rate. It first subtracts resting rate from maximum to obtain reserve, multiplies that reserve by a zone fraction, and adds resting rate back so two athletes who share the same ceiling but not the same baseline get different training bands. The engine then places five adjacent coaching bands on that reserve: recovery at fifty to sixty percent, endurance at sixty to seventy, tempo at seventy to eighty, threshold at eighty to ninety, and maximum at ninety to one hundred percent of heart-rate reserve. Send required hr_rest as a positive finite resting pulse in beats per minute; aliases hrrest, rest_hr, resting_hr, resting_heart_rate, and rhr are accepted. Send required hr_max as a positive finite maximum pulse; aliases hrmax, max_hr, maximum_heart_rate, and hrm are accepted. Maximum must be strictly greater than rest—equal or inverted rates cannot describe a positive reserve and fail with invalid_input. Identical inputs always yield identical JSON because the algorithm never touches the network, a model, a clock, or a random generator. Missing fields, empty strings, non-finite values, non-positive bpm, unrealistic rates above the isolate ceiling, and inverted pairs all fail with invalid_input and are not charged.

Reading the five zones and how each bound is computed

Use a true morning resting pulse after several minutes of quiet sitting, not a mid-day walking average. On success the response echoes hr_rest and hr_max after normalisation, reports hrr as heart-rate reserve in beats per minute, and sets unit to bpm so UIs can label numbers without hard-coding strings. The method field is always percent_hrr and formula restates zone bpm equals resting rate plus percent times the gap between maximum and rest. zone_count is five. Each zone is also flattened for forms and dashboards: zone1_name through zone5_name hold recovery, endurance, tempo, threshold, and maximum; zoneN_pct_lo and zoneN_pct_hi hold the percent-of-reserve edges; zoneN_bpm_lo and zoneN_bpm_hi hold the matching pulses. The zones array repeats the same five records in order, each with zone, name, pct_lo, pct_hi, bpm_lo, and bpm_hi, so a table renderer can walk one list. Adjacent bands share a boundary by design: the top of recovery is the bottom of endurance, and so on up to maximum, which always ends at hr_max because one hundred percent of reserve plus rest is the ceiling you supplied. Prefer a measured peak from a maximal field or lab effort when you have one; if you only have an age-predicted ceiling, compute that client-side and pass the result as hr_max so this engine stays a pure reserve transform. Do not confuse this endpoint with a single Karvonen target at one intensity, with a percentage-of-max chart that ignores rest, or with age-only maximum estimators: those are different search intents and live in separate products.

API usage, pricing, coaching workflows, and practical limits

Call the free in-browser heart rate zones from reserve calculator for PE classes, club fitness days, and quick athlete checks without rebuilding the five-band percent-HRR table in a spreadsheet. 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 five-zone chart alone. Send a JSON body with required hr_rest and hr_max in beats per minute. 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-pulse protocol and an honest maximum source, then store the five bpm windows alongside date and conditions for session cards that say stay in endurance or climb into threshold. If your UI already collects resting_hr and max_hr under those names, send the documented aliases—the engine accepts them without a second mapping layer. Authors shipping SDKs can map zone1_bpm_lo through zone5_bpm_hi or the zones array into dashboards and export CSV columns labeled recovery, endurance, tempo, threshold, and maximum—the same numbers coaches compute by hand after recording rest and max bpm.