{
    "name": "Heart Rate Reserve Calculator",
    "url": "https://calculators.geekmidst.com/calculators/heart-rate-reserve-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/heart-rate-reserve-calculator.md",
    "category": "Health & fitness",
    "description": "Find your heart-rate reserve and what percentage of it a given exercise heart rate represents, using the Karvonen method and a measured or age-estimated maximum.",
    "summary": "Heart-rate reserve (HRR) is the gap between your maximum and resting heart rates. Enter the heart rate you saw during exercise to see the share of your reserve you were using.",
    "also_called": [
        "HRR calculator",
        "%HRR calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "max_formula",
            "label": "Maximum heart rate from",
            "type": "select",
            "default": "tanaka",
            "options": {
                "tanaka": "Tanaka: 208 − 0.7 × age",
                "fox": "Traditional: 220 − age",
                "measured": "My measured maximum"
            }
        },
        {
            "name": "age",
            "label": "Age",
            "type": "number",
            "default": "40",
            "unit": "years",
            "shown_when": {
                "max_formula": [
                    "tanaka",
                    "fox"
                ]
            }
        },
        {
            "name": "max_hr",
            "label": "Measured maximum heart rate",
            "type": "number",
            "default": "185",
            "unit": "bpm",
            "shown_when": {
                "max_formula": "measured"
            }
        },
        {
            "name": "resting_hr",
            "label": "Resting heart rate",
            "type": "number",
            "default": "60",
            "unit": "bpm"
        },
        {
            "name": "exercise_hr",
            "label": "Exercise heart rate",
            "type": "number",
            "default": "132",
            "unit": "bpm"
        }
    ],
    "outputs": [
        {
            "key": "pct_hrr",
            "label": "Intensity (% of heart-rate reserve)",
            "format": "percent"
        },
        {
            "key": "reserve",
            "label": "Heart-rate reserve",
            "format": "integer"
        },
        {
            "key": "max_hr",
            "label": "Maximum heart rate used",
            "format": "integer"
        },
        {
            "key": "pct_max",
            "label": "Percentage of maximum heart rate",
            "format": "percent"
        }
    ],
    "formula": {
        "text": "HRR = HRmax − HRrest;  %HRR = (HRexercise − HRrest) ÷ HRR × 100;  HRmax (Tanaka) = 208 − 0.7 × age",
        "variables": {
            "HRmax": "maximum heart rate, measured or estimated from age",
            "HRrest": "resting heart rate",
            "HRexercise": "heart rate during the activity"
        }
    },
    "worked_example": {
        "inputs": {
            "max_formula": "tanaka",
            "age": "40",
            "max_hr": "185",
            "resting_hr": "60",
            "exercise_hr": "132"
        },
        "steps": [
            "HRmax = 208 − 0.7 × 40 = 180 bpm.",
            "HRR = 180 − 60 = 120 bpm.",
            "%HRR = (132 − 60) ÷ 120 = 60%."
        ],
        "result": "At 132 bpm, a 40-year-old with a resting heart rate of 60 is working at 60% of heart-rate reserve."
    },
    "interpretation": "%HRR tracks oxygen uptake more closely than %HRmax, which is why exercise guidelines often express intensity as a share of reserve. Use the Target Heart Rate Calculator to turn a chosen intensity into a heart-rate range.",
    "assumptions": [
        "Age-predicted maximum heart rate is a population average; an individual can differ by 10 bpm or more.",
        "Resting heart rate is measured at genuine rest."
    ],
    "limitations": [
        "Beta-blockers and some other medicines lower heart rate and make these percentages misleading.",
        "Heat, dehydration and fatigue raise heart rate for the same effort."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "What is the Karvonen method?",
            "answer": "It sets exercise intensity as a percentage of heart-rate reserve and adds back the resting rate: target = rest + intensity × (max − rest)."
        },
        {
            "question": "Why does %HRR differ from %HRmax?",
            "answer": "Because %HRmax starts from zero rather than from your resting rate, it always gives a higher figure for the same heartbeat."
        }
    ],
    "sources": [],
    "related": [
        {
            "name": "Target Heart Rate Calculator",
            "url": "https://calculators.geekmidst.com/calculators/target-heart-rate-calculator"
        },
        {
            "name": "Calories Burned Calculator",
            "url": "https://calculators.geekmidst.com/calculators/calories-burned-calculator"
        },
        {
            "name": "Walking Speed Calculator",
            "url": "https://calculators.geekmidst.com/calculators/walking-speed-calculator"
        }
    ],
    "disclaimer": "This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health.",
    "publisher": "GM¹X CalcVerse"
}