How the calculators work
Everything is calculated in your browser. Nothing you type is sent to a server or stored, and the pages work the same with a fresh browser.
| What | Formula | Source |
|---|---|---|
| Maximum heart rate | 208 − 0.7 × age; 220 − age for comparison | Tanaka et al. 2001; Fox et al. 1971 |
| Zone 2, % of max | 60–70 % of maximum | Five-zone model |
| Zone 2, reserve | rest + 60–70 % × (max − rest) | Karvonen et al. 1957 |
| Zone 2, MAF | 180 − age ± adjustment, 10 beats below | Maffetone |
| Zone 2, threshold | 85–89 % of LTHR running, 81–89 % cycling | Friel |
| Zone 2, power | 56–75 % of FTP | Coggan |
| Walking oxygen cost | 0.1·S + 1.8·S·G + 3.5 ml/kg/min | ACSM |
| VO₂max estimate | 15.3 × max HR ÷ resting HR | Uth et al. 2004 |
| Heart rate vs oxygen | % of HR reserve ≈ % of VO₂ reserve | Swain & Leutholtz 1997 |
| Weekly minutes | 150–300 moderate, or 75–150 vigorous | WHO 2020 |
Pages show results for default inputs even without JavaScript; the numbers are produced by the same code that runs in your browser.
Sources
- Tanaka, Monahan & Seals (2001). Age-predicted maximal heart rate revisited. J Am Coll Cardiol. pubmed.ncbi.nlm.nih.gov
- The science of exercise prescription: Martti Karvonen and his contributions. BC Medical Journal. bcmj.org
- Maffetone, P. The MAF 180 Formula. philmaffetone.com
- Friel, J. Joe Friel's quick guide to setting zones. TrainingPeaks. www.trainingpeaks.com
- Coggan, A. Power training levels. TrainingPeaks. www.trainingpeaks.com
- American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription: metabolic equations.
- Uth et al. (2004). Estimation of VO2max from the ratio between HRmax and HRrest: the Heart Rate Ratio Method. Eur J Appl Physiol. pubmed.ncbi.nlm.nih.gov
- Swain & Leutholtz (1997). Heart rate reserve is equivalent to %VO2 reserve, not to %VO2max. Med Sci Sports Exerc. pubmed.ncbi.nlm.nih.gov
- Bull et al. (2020). World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med. pmc.ncbi.nlm.nih.gov
- Martin et al. (2025). Exploratory analysis of the accuracy of age-based maximal heart rate equations across cardiorespiratory fitness levels. PLoS One. pmc.ncbi.nlm.nih.gov
- Eston & Connolly (1996). The use of ratings of perceived exertion for exercise prescription in patients receiving beta-blocker therapy. Sports Med. pubmed.ncbi.nlm.nih.gov
Limits
These are population formulas. They describe averages, and a single person can sit well above or below them. Heart rate also drifts with heat, caffeine, sleep, stress and dehydration. If you take medication that lowers heart rate (beta-blockers or some calcium-channel blockers, for example) or have a heart condition, the formulas don't apply to you: ask your doctor, and use perceived effort instead. Nothing here is medical advice.
Who makes it
zone2.fit is made by Alexey Zhuchkov in Barcelona, Spain. Corrections and questions are welcome at hello@zone2.fit. The site has no ads and no affiliate links; if that changes, such links will be clearly labelled.
Privacy
There is no sign-up, no form that collects personal data and no tracking cookies. The site is hosted by Cloudflare, which keeps technical logs (IP address, requested page) for a few days for security, as a data processor. Visits are counted with Cloudflare Web Analytics, which uses no cookies or identifiers. Controller: Alexey Zhuchkov, contact above. Legal basis: legitimate interest in running and securing the site. You can exercise your rights of access, rectification, erasure, objection, restriction and portability by writing to hello@zone2.fit, and complain to the Spanish Data Protection Agency (aepd.es).