MariposasHeart Rate Zone Calculator
By Zachary, builder of Mariposas · Reviewed against published exercise-science sources (references)
· Last updated June 2026
Cardio & Running | Zone | Heart rate |
|---|---|
| Zone 1, Recovery | 94-112 bpm |
| Zone 2, Easy | 112-131 bpm |
| Zone 3, Aerobic | 131-150 bpm |
| Zone 4, Threshold | 150-168 bpm |
| Zone 5, Max | 168-187 bpm |
Add resting HR for more accurate Karvonen zones.
Training by heart-rate zone keeps easy days easy and hard days hard. This calculates your max heart rate (Tanaka) and five zones, add your resting heart rate for more accurate Karvonen zones.
⚕️ A general-information estimate from population-level formulas, a starting point, not a precise measurement and not medical advice.
How it works
The calculator uses the Tanaka formula, published in the Journal of the American College of Cardiology in 2001, to estimate maximum heart rate: 208 minus 0.7 times your age. Tanaka's research on over 500 subjects found this formula more accurate across age groups than the older 220-minus-age rule, which tends to overestimate max HR in younger people and underestimate it in older adults. Once max HR is established, the five training zones are carved out as percentages of that ceiling. If you supply a resting heart rate, the calculator switches to the Karvonen method, which works off your heart rate reserve (max HR minus resting HR) and adds resting HR back in at the end. Because heart rate reserve reflects how much cardiac output you actually have available to work with, Karvonen zones sit slightly higher in absolute BPM terms than percentage-of-max zones, and many coaches consider them more individually accurate for trained athletes whose resting HR is low.
When to use it
This calculator is useful any time you want to structure a training week around effort rather than pace or feel alone, whether you're preparing for an endurance event, adding structured cardio to a strength program, or simply trying to avoid the common trap of doing every run at the same moderate intensity. It's especially helpful when you know your true resting HR from a week of morning measurements, because that single extra input meaningfully shifts your zone boundaries compared to a pure age-based estimate.
Worked example
Take a 38-year-old with a resting heart rate of 58 BPM. The Tanaka formula gives a max HR of 208 minus (0.7 times 38), which equals 181 BPM. Using the Karvonen method, the heart rate reserve is 181 minus 58, or 123 BPM. Zone 2 (the aerobic base zone, roughly 60 to 70 percent of reserve) then runs from about 132 to 144 BPM after adding resting HR back in. If that same person only used a flat 60 to 70 percent of max HR, Zone 2 would be 109 to 127 BPM, noticeably lower, and many sessions that genuinely feel aerobic would be miscategorized as too easy.
Tips for an accurate result
- Measure resting HR first thing in the morning before getting out of bed, ideally across three to five consecutive days and averaging the results. A single reading after a poor night of sleep can be 10 or more BPM above your true baseline.
- The Tanaka formula is an estimate. If you have done a true maximal effort test (a graded treadmill test or an all-out field test like a 3-mile time trial), use that measured value instead of the formula output for more precise zones.
- Understand what each zone is actually training before you program around it. Zone 1 and 2 build mitochondrial density and fat oxidation. Zone 4 and 5 work anaerobic threshold and VO2 max. Spending most of your volume in Zone 3 (comfortably hard) is a common mistake that leaves athletes chronically fatigued without meaningful adaptation in either direction.
- Heart rate lags behind effort by roughly 30 to 60 seconds, so on intervals shorter than two minutes you may never see your true zone reflected on the monitor. Rate of perceived exertion fills that gap better for very short efforts.
- Caffeine, dehydration, heat, and sleep debt all elevate heart rate at any given workload. If a familiar easy run has your HR running 10 to 15 BPM higher than usual, the zone numbers are less meaningful that day than how your legs and breathing feel.
Formula & sources: methodology · references.
Now go hit the number Mariposas turns every workout, run and class into progress · collect a cute pet 🐾FAQ
- Why does the Tanaka formula give a different max HR than 220 minus my age?
- The 220-minus-age formula originated from a rough visual fit of existing data in the early 1970s and was never intended as a precise clinical tool. Tanaka's team did a formal meta-analysis and regression across a wide age range and found the relationship between age and max HR is better captured by the shallower slope of 208 minus 0.7 times age. For a 25-year-old the two formulas give nearly the same number, but by age 60 the gap is meaningful enough to push you into the wrong zone.
- What is a 'good' resting heart rate to enter?
- For most adults, resting HR falls somewhere between 50 and 80 BPM. Highly trained endurance athletes sometimes sit in the low 40s. What matters for this calculator is accuracy rather than a target number. Measure it consistently before rising in the morning and use an average. Entering a resting HR of 72 when your true baseline is 58 will compress your Karvonen zones in a way that undervalues your aerobic capacity.
- My GPS watch already shows heart rate zones. Why use this calculator?
- Most wearables default to straight percentage-of-max-HR zones, and many use 220 minus age to estimate your max rather than asking you to input a measured value. If you've never changed those defaults, there's a good chance the device zones don't match your actual physiology. Running your own numbers gives you zone boundaries you can then manually enter into most devices.
- How often should I recalculate my zones?
- Age creeps the Tanaka max HR estimate down by about 0.7 BPM per year, so annual recalculation is reasonable for most people. Resting heart rate can shift faster, especially during a dedicated training block where aerobic fitness improves, so checking it every few months and updating that input is worthwhile. After a major illness, significant weight change, or a long training break, a fresh calculation makes sense.
- Can I use these zones for cycling or swimming, not just running?
- Heart rate zones are modality-specific in practice. Cycling max HR typically runs 5 to 10 BPM lower than running max HR because less muscle mass is involved and there's no impact loading the cardiovascular system the same way. Swimming max HR can be lower still due to the horizontal position and cooler water. Zones calculated from a running max will likely place you in a perceived Zone 3 effort when the numbers say Zone 2 on a bike. Ideally you'd run a max effort test for each activity.