Zone 2 heart rate calculator

What does this calculator show?

This calculator turns your max heart rate into three training bands. Diastra calls them Easy, Threshold and VO₂max. Easy is the Zone 2 most people know, and its top edge comes from blood tests on runners.

A 2025 panel of 14 sport scientists and coaches agreed that Zone 2 training is best done right below the first lactate or breathing threshold.^[1] The first lactate threshold is called LT1. It is the point where lactate in your blood first starts to rise above its resting level. Easy ends where blood tests on runners find that point on average.

The space between Easy and Threshold is called the gray band. The hardest band is VO₂max, and it starts where Threshold ends. VO₂max is also the name for the most oxygen your body can use when you go all out. What Zone 2 heart rate means covers the idea behind the bands.

How the math works

1. Your max. The calculator uses the Tanaka formula when it has only your age. Your max is 208 minus 0.7 times your age.^[2] If you type a max from a race or a test, the calculator uses your number.
2. Easy. Easy starts at 60% of your max. It ends one beat under 79% of max for men, 83% for women and 80% when sex is left blank.
3. Threshold. Threshold starts at 87% of your max and ends one beat under 92%.
4. VO₂max. VO₂max starts at 92% of your max and runs up to your max.
5. Whole beats. Every edge rounds up to a whole beat. The first beat in each band is the first beat that reaches its percentage.

Take a 40-year-old who has never measured a max. The formula gives 208 minus 28, which is 180. A man's Easy runs from 108 to 142 beats a minute. A woman's Easy runs from 108 to 149. Threshold runs from 157 to 165 for both, and VO₂max starts at 166.

Why does Zone 2 end higher here than on many charts?

Many heart rate charts put Zone 2 at 60 to 70% of max. The 70% line for the 40-year-old above is 126 beats a minute.

Blood tests put the first threshold higher on average. Nuuttila and colleagues tested 165 runners on a treadmill.^[3] They were 20 to 50 years old, and all of them ran regularly. The women reached LT1 at 83.6% of max on average. The men reached it at 78.9%. Easy's top comes from those two numbers, so it ends at 79% for men and 83% for women. When sex is left blank, Easy ends at 80%. That edge is close to the 80.7% average of all 165 runners.

Breathing tests show the same split. Benítez-Muñoz and colleagues tested more than 1,200 people on a treadmill.^[4] They measured VT1, the first breathing threshold. It is the point where your breathing starts to climb faster than the work. The women's average share of max was higher than the men's at every training level.

Coaches and athletes draw their line in about the same place. A 2025 survey asked endurance coaches and athletes where each zone on their five-zone scale starts.^[5] Runners started zone 2 at 69.8% of max on average and zone 3 at 79.6%. So the zone 2 that runners use tops out near 80% of max.

A scale used for world-class distance runners shows the gap from another side.^[6] Its lowest zone runs from 60 to 72% of max. The paper lists it for warm-ups, cool-downs and easy long runs. The next zone up runs from 73 to 82%, and the paper lists it for long runs, uphill runs and progressive runs. That scale treats both zones as low intensity. Easy's 60% floor matches the bottom of its lowest zone.

Where do the Threshold and VO₂max edges come from?

Threshold is named for LT2, the second lactate threshold. Above LT2, lactate in your blood climbs steeply. The 165 runners in the lactate study reached LT2 at 90.6% of max on average.^[3] The women averaged 91.7% and the men 89.9%. Diastra's Threshold band runs from 87 to 92% of max, so all three averages fall inside it.

The same survey puts its upper lines in nearly the same places.^[5] Runners started zone 4 at 86.6% of max on average and zone 5 at 92.3%. Diastra starts Threshold at 87% and VO₂max at 92%. Both edges are less than 1% of max away from the runners' averages.

VO₂max starts at the same 92% line where Threshold ends. No beat falls between the two bands. The name tells you what the band trains. It does not mean every minute in the band is spent at your VO₂max.

How far off can a research edge be for you?

Each edge is an average. Your own line can land somewhere else.

Nuuttila's team tested this directly. They gave each runner the average LT1 percentage for their sex. They applied it to the max each runner reached on the treadmill.^[3] The real LT1 fell within about 16 beats above or below that estimate for 95 of every 100 runners. LT2 was tighter, and it fell within about 9 beats.

Sixteen beats is a wide miss. It is about 9% of a 180 max. That is wider than the whole gray band for a man with that max.

The same study checked a fixed line at 80% of max. At that line, 57 of every 100 runners were still below their own LT1. The other 43 were already above it.^[3]

The line also differs with training. The breathing study grouped people by how trained they were.^[4] Men with the least training reached VT1 at 74.6% of max on average. Men with the most training reached it at 80.8%. The authors wrote that a fixed percentage of max “might not be effective” for matching effort across people.

So read your bands as a starting map. Easy should feel easy, and you should be able to talk in full sentences. Slow down when you cannot, even if the number still reads Easy.

Why does a real max matter more than your age?

Every band is a percentage of your max. A wrong max moves every edge with it.

An age formula gives the average max of the people in its studies. Tanaka built the formula from 351 studies with 18,712 people, then checked it on 514 more in the lab.^[2] Your own max can still be far from it.

A later study measured the max of 3,320 healthy adults with an all-out exercise test.^[7] It built its own age formula from those tests. Even that formula left a wide spread. Its standard error was 10.8 beats a minute. That means a real max often landed 11 or more beats above or below the formula's guess.

Take the 40-year-old again. The formula says 180. Say a hard race shows a real max of 191, which is 11 beats higher. A man's Easy now ends at 150 beats a minute. Threshold moves up to 167 to 175, and VO₂max starts at 176. Every edge moves up by 7 to 10 beats.

The lactate study saw the same problem. Its thresholds were harder to predict when the max came from the Tanaka formula than when it came from the treadmill.^[3]

The table below shows the bands the age formula gives from age 20 to 70. Use it as a first guess until you know your real max.

Beats a minute, with max heart rate estimated from age (Tanaka). A measured max moves every band.

How do you find your real max?

Your max shows up at the end of your hardest efforts. Three sources can give you one.

• A guided max test. You warm up, then raise the pace in steps until you cannot go faster. The top heart rate near the end is your max.
• Your hardest days. The finish of a hard race or the last rep of a hard interval session can come close to your max.
• A typed number. A max from a past lab test works too.

A single high spike on a watch is not a max. Wrist sensors can jump for a second. A real max holds for several seconds, and a similar number shows up again on another hard day.

An all-out effort is strenuous. Try one only if you already train hard and feel fresh that day. How to find your max heart rate on Apple Watch covers this step by step. The max heart rate calculator compares the age formulas.

What should you do with your numbers?

Run most of your week in Easy. World-class distance runners do at least 80% of their running at low intensity all year round.^[6]

A 2007 study tested a mostly easy mix in runners. It split 12 trained runners into two groups for five months.^[8] One group did 80.5% of its training below the first breathing threshold. The other group did 66.8% there and more of its training between the two thresholds. The share of very hard work was about the same in both groups. Both groups ran a 10.4 km race faster. The mostly easy group improved by 157 seconds, and the other group improved by 121.5 seconds.

Easy is a wide band. Run wherever in it feels easy that day. Keep Threshold and VO₂max for a few planned hard sessions.

To see these numbers on your wrist during a run, read heart rate zones on Apple Watch.

How does Diastra draw your bands?

Diastra does this math from your own Apple Watch workouts. It reads every workout your watch saved in Apple Health. It finds your max heart rate from your hardest efforts, a guided test or a number you type, and it tells you which one it used. Easy, Threshold and VO₂max come from that max, and Easy's top edge is split by sex. The watch taps your wrist when you drift out of your band on a run. Only the minutes that held get credit, and Diastra shows over the weeks whether your training is working. The full method is in how Diastra draws your bands.