Heart Rate Zone Calculator
Your five training zones, and, more usefully, what each one is actually for.
In short
Training zones are percentages of your maximum heart rate, or of your heart rate reserve if you know your resting rate. The common 220-minus-age estimate for maximum has a standard deviation of about 10–12 beats, so a measured maximum is considerably more useful than a calculated one.
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What each zone is for
The numbers are only useful if you know what to do with them. Broadly:
| Zone | Effort | What it develops |
|---|---|---|
| 1, Recovery | Very easy, full conversation | Blood flow and recovery between hard sessions. Genuinely easy. |
| 2, Endurance | Easy, comfortable conversation | Aerobic base, fat oxidation, capillary density. Where most training time should go. |
| 3, Tempo | Moderate, short sentences | Aerobic capacity. Useful in moderation, and the zone people accidentally live in. |
| 4, Threshold | Hard, a few words | Lactate threshold, the pace you can hold for about an hour. |
| 5, Maximum | Very hard, no talking | VO₂ max and top-end power. Short intervals only. |
The mistake almost everyone makes
Spending most of their training in zone 3.
It feels productive, you're working, you're sweating, you finish tired. But it's too hard to build a proper aerobic base and too easy to drive real high-end adaptation. You accumulate fatigue without the benefit of either end.
The pattern that consistently shows up in endurance research is roughly 80% easy, 20% hard, with very little in between. That means your easy runs should feel almost embarrassingly slow, and your hard sessions genuinely hard.
Most people find the easy part harder than the hard part. Running slowly enough to hold a conversation, when you know you could go faster, takes more discipline than an interval session.
Maximum, and why 220 minus age is weak
The 220-minus-age formula is everywhere because it's easy to remember. Its standard deviation is about 10–12 beats, which means a 40-year-old's true maximum could plausibly sit anywhere between 160 and 200.
Build zones on an estimate that's 15 beats out and every zone is 15 beats out. Some
alternatives fit the data slightly better, Tanaka's 208 − 0.7 × age is
commonly cited. But all of them are population averages describing a wide distribution.
If you've ever seen a genuine maximum during a hard effort, the highest number on a race finish or a brutal hill session. Enter it. A measured maximum turns approximate zones into meaningful ones.
Why Karvonen usually fits better
Percentage-of-maximum ignores your resting heart rate, and that matters. Karvonen works from your heart rate reserve: the gap between resting and maximum:
Target = ((max − resting) × intensity) + restingTwo people with the same maximum but resting rates of 45 and 70 have quite different capacities, and Karvonen reflects that. The difference is most pronounced at the easy end, where percentage-of-maximum tends to set zone 2 unrealistically low for fit people.
Things that shift your heart rate on the day
Heart rate is a response, not a fixed dial. On any given day it can be pushed around by:
- Heat and humidity: often 5–10 beats higher for the same effort.
- Dehydration: reduced blood volume means a faster heart.
- Caffeine: a few beats up.
- Poor sleep or illness: an elevated resting rate is one of the earliest signs of coming down with something.
- Cardiac drift: heart rate creeps up over a long session at constant effort.
- Stress and altitude: both raise it.
- Medication. Beta blockers substantially lower both resting and maximum, which makes standard zones meaningless.
Which is why perceived effort still matters. If the zone says easy and it feels hard, trust the feeling and slow down, that's information about your recovery, not a malfunctioning watch.
Training guidance, not medical advice. If you have a heart condition, take medication affecting heart rate, or experience chest pain, dizziness or unusual breathlessness, speak to a doctor before following any of this.
Frequently asked questions
How do I find my maximum heart rate?
The 220-minus-age estimate is convenient and imprecise. Its standard deviation is about 10–12 beats, so a 40-year-old's true maximum could plausibly be anywhere from 160 to 200. If you have ever seen a genuine maximum on a hard effort, enter that instead; it makes every zone meaningful rather than approximate.
What is the Karvonen method?
It calculates zones from your heart rate reserve: the gap between resting and maximum, rather than from maximum alone. Because it accounts for fitness, it usually produces more realistic zones, especially for well-trained people whose resting rate is low.
How do I measure my resting heart rate?
Take it first thing in the morning, before getting out of bed and before caffeine. Count for 60 seconds, or use a wearable's overnight figure. Average three or four mornings. A single reading is noisy, and one poor night can shift it by ten beats.
Should I train in one zone or several?
Most endurance research points to spending roughly 80% of training time in the easy zones and 20% hard, with little in the middle. The common failure is making easy days too hard and hard days too easy, so everything ends up moderately uncomfortable and nothing improves much.
Is this medical advice?
No. Heart rate zones are training guidance, not a health assessment. If you have a heart condition, take medication affecting heart rate, beta blockers in particular lower both resting and maximum substantially, or experience chest pain or unusual breathlessness, speak to a doctor before using these numbers.