The measurement taken immediately after waking up, before getting out of bed.
Male
Female
Estimated Resting Heart Rate
— BPM
function calculateFitbitRHR() {
// 1. Get input values
var sleepHR = document.getElementById('avgSleepHR').value;
var wakingHR = document.getElementById('wakingHR').value;
var age = document.getElementById('userAge').value;
var gender = document.getElementById('userGender').value;
var resultArea = document.getElementById('result-area');
var rhrDisplay = document.getElementById('rhrResult');
var assessmentDisplay = document.getElementById('healthAssessment');
// 2. Validate inputs
if (sleepHR === "" || wakingHR === "" || age === "") {
alert("Please fill in all heart rate and age fields to calculate.");
return;
}
var sleepNum = parseFloat(sleepHR);
var wakingNum = parseFloat(wakingHR);
var ageNum = parseInt(age);
if (isNaN(sleepNum) || isNaN(wakingNum) || isNaN(ageNum) || sleepNum <= 0 || wakingNum <= 0) {
alert("Please enter valid positive numbers for heart rate.");
return;
}
// 3. Calculation Logic mimicking Fitbit's aggregation
// Fitbit uses multiple data points throughout the night and morning.
// It heavily weights the 'sleeping' HR but factors in the 'waking' HR for stability.
// We simulate this with a weighted average favoring sleep data (60/40 split approximation).
var calculatedRHR = (sleepNum * 0.6) + (wakingNum * 0.4);
calculatedRHR = Math.round(calculatedRHR);
// 4. Assessment Logic based on Age and Gender Norms (General AHA/Fitbit data)
var fitnessLevel = "Average";
var description = "";
// Simple lookup logic for assessment
if (gender === "male") {
if (calculatedRHR < 60) {
if (ageNum < 50) fitnessLevel = "Athlete / Excellent";
else fitnessLevel = "Excellent";
} else if (calculatedRHR <= 65) {
fitnessLevel = "Good";
} else if (calculatedRHR <= 70) {
fitnessLevel = "Average";
} else {
fitnessLevel = "Below Average";
}
} else {
// Female rates are typically slightly higher
if (calculatedRHR < 65) {
if (ageNum < 50) fitnessLevel = "Athlete / Excellent";
else fitnessLevel = "Excellent";
} else if (calculatedRHR <= 70) {
fitnessLevel = "Good";
} else if (calculatedRHR <= 75) {
fitnessLevel = "Average";
} else {
fitnessLevel = "Below Average";
}
}
// Specific Fitbit context
if (calculatedRHR 90) {
description = "Your RHR is elevated. This can be caused by stress, caffeine, dehydration, or illness.";
} else {
description = "Your estimated RHR is within a standard range for your demographic.";
}
// 5. Display Results
resultArea.style.display = "block";
rhrDisplay.innerHTML = calculatedRHR + " BPM";
assessmentDisplay.innerHTML = "Fitness Category: " + fitnessLevel + "" + description;
}
How Fitbit Calculates Resting Heart Rate
Understanding your Resting Heart Rate (RHR) is one of the most effective ways to gauge your overall cardiovascular health and fitness levels. Unlike a standard heart rate reading taken at a random time of day, your Fitbit uses a specific methodology to calculate RHR to ensure accuracy and consistency.
The Technology: Photoplethysmography (PPG)
Fitbit devices use optical heart rate sensors located on the back of the device. This technology, known as photoplethysmography (PPG), involves flashing green LED lights onto the skin. Since blood is red, it reflects red light and absorbs green light.
When your heart beats, the blood flow in your wrist increases, absorbing more green light. Between beats, it decreases. By flashing these LEDs hundreds of times per second, Fitbit calculates the number of times your heart beats per minute (BPM).
The Calculation Logic
Fitbit does not simply take a snapshot of your heart rate while you are sitting on the couch. The calculation is more complex and designed to eliminate outliers caused by momentary stress or movement.
Sleep Data is Critical: Fitbit places the highest priority on heart rate data collected while you are asleep. During deep sleep, your body is in its most relaxed state, providing the purest baseline for heart function.
Waking Measurement: The device also monitors your heart rate immediately upon waking but before you get out of bed. This "morning pulse" is a traditional method for measuring RHR manually.
The Aggregation: Fitbit combines the lowest sustained heart rate readings from your sleep cycle with the data captured upon waking to generate a single daily RHR figure.
Why is my Fitbit RHR different from my doctor's reading?
A doctor usually measures your heart rate while you are sitting upright and awake during the day. This is technically a "sedentary" heart rate, which is often 5-10 BPM higher than a true "resting" heart rate calculated during sleep.
Factors That Influence Your Numbers
If you notice a sudden spike or drop in your Fitbit's RHR calculation, consider these variables:
Alcohol and Caffeine: Consuming alcohol or caffeine late in the day can keep your heart rate elevated throughout the night, resulting in a higher RHR the next morning.
Overtraining: If you exercise heavily without adequate recovery, your sympathetic nervous system may remain active, keeping your RHR high.
Dehydration: A lack of fluids decreases blood volume, forcing the heart to beat faster to circulate oxygen.
Stress and Sleep Quality: Poor sleep cycles or high anxiety levels will prevent your heart rate from reaching its lowest potential baseline during the night.
Interpreting Your Score
Generally, a lower resting heart rate indicates better cardiovascular fitness and more efficient heart function. Professional athletes often have RHRs below 50 BPM. For the general population, a RHR between 60 and 80 BPM is considered normal, though this varies significantly by age and gender.