Heart Rate Zones Calculator

How the zones are calculated

This tool gives you two methods. Karvonen uses heart-rate reserve (HRmax − resting HR) and is the more individualised calculation — it accounts for the fact that two runners with the same HRmax but different resting heart rates are working at different intensities at the same bpm. % HRmax is simpler and matches how most fitness watches calculate zones.

If you provide a resting heart rate, Karvonen is recommended. If you only know your age, % HRmax works.

The Karvonen formula: target HR = resting HR + (HRmax − resting HR) × intensity%.

The five-zone model used here is the international standard adopted by Coggan, Friel, and most coaching platforms. Some coaches use seven zones — those are subdivisions of the same intensity bands.

The five zones in practice

Zone 1 (50–60%) is recovery pace. Run between hard workouts or before a quality session. Most runners drift out of Zone 1 within a few minutes — staying disciplined here is harder than it sounds.

Zone 2 (60–70%) is the aerobic base. This is the zone for the vast majority of your weekly mileage. You should be able to hold a conversation in complete sentences. If you find yourself out of breath, you’re in Zone 3 — slow down.

Zone 3 (70–80%) is the “no man’s land” of running. It corresponds to marathon and half marathon race pace. Too hard for daily training, too easy for stimulus when used in isolation. Race here, but don’t train here.

Zone 4 (80–90%) is threshold work — tempo runs and lactate-threshold intervals. You can sustain it for about an hour at the lower end, 20–40 minutes at the upper end. This is the zone where threshold workouts pay off.

Zone 5 (90–100%) is VO2 max work — short intervals of 2–5 minutes with equal recovery. Painful, brief, transformative when used 1–2× per week during a focused training block.

Heart rate vs pace

Heart rate measures your cardiovascular load. Pace measures your output. They diverge in three situations: heat, hills, and cumulative fatigue. On a 30 °C day, an easy-pace run can drift into Zone 3 on HR. On a hilly course, your watch shows slow pace but HR tells you you’re working hard.

The practical pairing: use pace zones from the VDOT Calculator for the workout structure (e.g. “5 × 1K at threshold pace”), and use HR zones as a sanity check on effort. When the two disagree, trust HR for effort and trust pace for distance/time targets.

When zones become unreliable

Three failure modes:

Inaccurate HRmax. If your estimated HRmax is 8 bpm too high, every zone shifts up. A field test (described in the Max HR Calculator notes) gives the accurate number.

Cardiac drift. During a long run in heat, HR drifts up by 5–15 bpm at the same effort and pace as your body redirects blood to skin for cooling. Don’t slow down — you’re still running the same intensity.

Caffeine, sleep, illness. Resting HR rises 5–10 bpm when under-recovered. If your easy run is showing Zone 3 HR at your normal Zone 2 pace, take an easy day or rest.

Want all of this in your pocket, offline, with no subscription? Pacesmith is a $1.99 iOS app — VDOT zones, race predictions, pace math, and split planning, no internet required, one-time purchase.