The average heart rate during sleep for a healthy adult is about 50 to 75 beats per minute, which is noticeably lower than the typical daytime resting rate of 60 to 100 bpm. Your heart slows down during sleep because your body’s demand for oxygen drops, your nervous system shifts into recovery mode, and your muscles are largely inactive. But that number isn’t static through the night. It rises and falls depending on which stage of sleep you’re in, and several personal factors can push it higher or lower.
How Heart Rate Changes Through the Night
Your heart doesn’t simply settle at one speed when you fall asleep. Within about five minutes of drifting off, it begins gradually slowing as you enter light sleep. This is your body’s transition period, and the drop is modest.
The real slowdown happens during deep sleep. In this stage, your blood pressure falls and your heart rate drops to roughly 20% to 30% below your normal resting rate. For someone with a daytime resting rate of 70 bpm, that could mean a heart rate in the low 50s or even the upper 40s. Deep sleep is when your body does its most intensive repair work, and the cardiovascular system gets a genuine break.
REM sleep, the stage associated with vivid dreaming, is a different story. Your heart rate during REM can fluctuate significantly because it mirrors the content of your dreams. A stressful or action-filled dream can push your heart rate up to near-waking levels, while a calm dream keeps it lower. This variability is normal and not a sign of a problem. Most people cycle through these stages four to six times per night, so your heart rate follows a wave-like pattern rather than a flat line.
Normal Ranges by Age
Children have significantly faster heart rates than adults, both awake and asleep. Typical resting heart rates by age group look like this:
- Newborns (birth to 4 weeks): 100 to 205 bpm
- Infants (4 weeks to 1 year): 100 to 180 bpm
- Toddlers (1 to 3 years): 98 to 140 bpm
- Preschool age (3 to 5 years): 80 to 120 bpm
- School age (5 to 12 years): 75 to 118 bpm
- Adolescents (13 to 17 years): 60 to 100 bpm
- Adults (18+): 60 to 100 bpm
These are awake resting rates. During sleep, expect numbers somewhat lower across every age group. A sleeping toddler with a heart rate of 90 bpm, for example, is perfectly normal even though that number would seem high for an adult.
Why Athletes Often See Much Lower Numbers
If you’re physically active and your sleep tracker shows a heart rate in the 40s, that’s likely nothing to worry about. Endurance training makes the heart more efficient, allowing it to pump the same volume of blood with fewer beats. A study of 465 endurance athletes found that 38% had a minimum heart rate at or below 40 bpm on a 24-hour monitor. A small number, about 2%, dropped to 30 bpm or below during sleep. These were predominantly young male cyclists, runners, and rowers.
Even rates below 35 bpm can be normal in elite athletes, though they become uncommon. The key distinction is whether a low heart rate comes with symptoms. An athlete who feels fine with a sleeping heart rate of 38 bpm is in a very different situation than a sedentary person experiencing the same number alongside dizziness or fatigue.
What Counts as Too High or Too Low
Broadly, any sleeping heart rate between 40 and 100 bpm falls within the range considered normal. Outside that window, the numbers alone don’t necessarily signal a problem, but they deserve attention.
A resting heart rate consistently above 100 bpm is classified as tachycardia. During sleep, this is more concerning than during the day because your body should be in its most relaxed state. Symptoms that accompany a fast sleeping heart rate, like waking up with a pounding chest, shortness of breath, dizziness, or feeling lightheaded, warrant prompt medical evaluation. Occasional spikes during REM sleep are normal, but a sustained elevated rate through the night is not.
On the low end, a heart rate that dips below 40 bpm in someone who isn’t physically trained could indicate an issue with the heart’s electrical system. Again, context matters. If you feel rested and have no symptoms like fainting or unusual fatigue, a low number on your sleep tracker may simply reflect your individual physiology.
Factors That Raise Your Sleeping Heart Rate
Room temperature has a direct effect. When your body is exposed to heat overnight, your heart works harder to circulate blood toward the skin surface for cooling. Research on adults aged 65 and over found that keeping bedroom temperatures around 24°C (75°F) reduced stress responses during sleep. Hotter rooms force the heart to sustain a higher rate for longer, which limits overnight recovery. For most adults, a bedroom between 18°C and 22°C (65°F to 72°F) is the range most conducive to a lower, steadier heart rate.
Alcohol is another common culprit. Even moderate drinking in the evening elevates your resting heart rate during the first half of the night as your body metabolizes the alcohol. Caffeine consumed too late in the day can have a similar, though usually milder, effect. Stress, illness, dehydration, and certain medications also push sleeping heart rate upward. If your tracker shows a sudden jump from your usual baseline, it can sometimes be the first sign that you’re fighting off an infection, even before other symptoms appear.
How to Track Your Sleeping Heart Rate
Most consumer wearables, including smartwatches and fitness bands, measure heart rate through optical sensors on your wrist. These are reasonably accurate for tracking trends over time, though they can occasionally misread during the night if the device shifts on your wrist. The most useful metric isn’t any single night’s reading. It’s your trend over weeks and months.
Pay attention to your personal baseline rather than comparing yourself to population averages. A sleeping heart rate of 55 bpm is perfectly healthy for one person and unusually high for another. What matters most is consistency. A gradual upward trend over weeks, or a sudden spike that doesn’t resolve, tells you more than any individual number. Many devices now report your lowest overnight heart rate or your average across the night, both of which are useful for spotting changes in your fitness, recovery, or overall health.