Your resting heart rate is how many times your heart beats per minute when you are doing nothing at all. It is free to measure, it takes a minute, and it tells you more about your aerobic fitness and your recovery than most of the numbers people pay for.
Why the number is useful
A trained heart moves more blood per beat, so it needs fewer beats to do the same job. That is why endurance athletes often sit in the 40s while a sedentary adult sits in the 70s.
The useful part is not the absolute figure. It is the direction it moves. Train consistently for a few months and you will watch it fall, which is direct evidence that the work is doing something, well before your race times catch up.
It also works in the other direction. A resting rate that climbs for several days is a good early warning that you are under-recovered, coming down with something, drinking too much, or sleeping badly. Your legs often feel fine on day one of that. The number does not.
Measuring it properly
Take it first thing in the morning, before you get out of bed and before coffee. That is the closest you get to a controlled condition.
Find your pulse at the wrist or the neck, count the beats for 30 seconds, and double it. A chest strap or a decent watch will do the same automatically, and most sleep-tracking devices report an overnight figure that works fine for trend-watching.
One reading tells you almost nothing. Take it several mornings a week and look at the average, because a single high morning after a late night is noise, not a signal.
What counts as a good number
Most adults land between 60 and 100. Regular exercisers are usually in the 50s or 60s, and well-trained endurance athletes go lower still.
But comparing yourself to a chart is the least interesting thing you can do with this metric. Genetics set a large part of where your baseline sits, and a naturally high resting rate in a fit person is not a fault. Compare yourself to yourself three months ago.
What moves it besides fitness
Plenty, which is why context matters.
Poor sleep raises it. So does psychological stress, through the same nervous system pathway. Dehydration raises it, because thinner blood volume means the heart works harder per beat. Alcohol reliably raises it overnight, and often for the night after as well. Caffeine and some medications push it up. Illness pushes it up before you feel ill.
Age nudges it upward over decades. Body composition plays a part too, though the fitness underneath usually explains more than the weight itself does.
Using it to steer your training
Treat a few days of elevated readings as information rather than a verdict. If your resting rate is five or more beats above your normal for two or three mornings running, that is a good day for an easy session instead of intervals.
The reverse is also worth acting on. A rate at or below your usual baseline, after a decent night's sleep, is your body telling you it can take a hard session. Most people have this backwards and push hardest on the days they feel worst about themselves.
Some watches also report heart rate variability, which measures the spacing between beats. Higher variability generally means better recovery. It is noisier than resting heart rate and needs a longer baseline before it means much, so start with the simpler number.
When to see a doctor
This is a fitness marker, not a diagnosis. A resting rate that stays above 100 without an obvious cause, or one that drops sharply without a corresponding jump in training, is worth a conversation with a doctor. So is a normal-looking rate alongside chest pain, breathlessness or fainting.
Sustained changes usually have a reason. Sometimes the reason is that your training is working. Sometimes it is not, and the point of watching the number is to notice the difference early.