An easy run should sit at 60–70% of your maximum heart rate, which is Zone 2. For a 35-year-old with an estimated max of about 184 bpm, that is 110–128 bpm. Without a strap, use the talk test: if you can’t speak in full sentences without gasping for the next word, you’re not running easy.
That estimated max comes from the Tanaka formula, 208 minus 0.7 times your age, derived from a meta-analysis of 351 studies. Plug your own age, or your measured max and resting heart rate, into the heart rate zones calculator for the exact numbers. The rest of this post is about why most runners miss both checks anyway, whatever the pace on the watch says.
What are the five heart rate zones?
The five heart rate zones run from Zone 1, recovery, at 50–60% of max, up to Zone 5, VO₂ max, at 90–100%. Easy running lives in Zone 2, at 60–70%. Add your resting heart rate and the calculation switches from the flat age-based estimate to the Karvonen method. Target heart rate equals resting rate plus reserve times the intensity percentage. That anchors the zones to your own fitness rather than to a population average.
The old 220-minus-age formula, still stapled to gym walls, has a typical error of about 7–11 bpm for an individual (Robergs & Landwehr, 2002), so your real max can sit 10–20 beats either side of it. That is wide enough to put someone’s real Zone 2 inside what their watch calls Zone 3. Tanaka’s formula tracks measured maximums more closely, especially in older runners. A measured max from a hard hill rep or a race finish beats either formula.
- Zone 1 — recovery (50–60%). Shakeout runs, the day after a hard session.
- Zone 2 — easy / aerobic (60–70%). Where most of a runner’s week should live.
- Zone 3 — tempo (70–80%). “Comfortably hard” — and where most easy runs actually end up.
- Zone 4 — threshold (80–90%). The edge of what you can sustain.
- Zone 5 — VO₂ max (90–100%). Short, sharp, reserved for intervals.
The gap between the two methods is not academic. Take a 40-year-old with a measured max of 180 bpm and a resting heart rate of 55 bpm: Karvonen puts their heart rate reserve at 125, so Zone 2 lands at 130–142 bpm. Estimate the same runner’s zones from max alone, no resting rate involved, and the range comes out at 108–126 bpm — roughly 20 beats lower at the bottom end. Neither number is wrong, but only the Karvonen one is describing this particular runner rather than a generic percentage of their ceiling. That gap is exactly why the calculator asks for a resting heart rate at all, and exactly why an easy run that “should” be 108 bpm by the simple formula can still feel wrong for someone whose real Zone 2 sits 20 beats higher.
Is the talk test accurate enough?
The talk test is accurate enough to catch most runs that drift out of Zone 2, and it makes a good cross-check on a strap. A heart rate number is only as good as the max it was calculated from, and most runners are working from a guess. That is what makes the talk test worth keeping even once you own a strap: if you can speak in full sentences, you are almost certainly in Zone 1 or 2, regardless of what an unverified max is telling the watch. If you can only manage a few words at a time, you have drifted into Zone 3 even if the display still reads a number that looks fine on paper. Use the two together — the bpm range as the target, the conversation as the sanity check on whether that range is actually right for you.
Why do most easy runs end up too fast?
Most easy runs end up too fast because real easy pace is slower than feels respectable. Easy pace is where runners fail the test they just passed on paper. A comfortable easy pace for many recreational runners sits around 6:00–7:00 per kilometre — noticeably slower than the pace that feels “normal” once a training log or a running club is involved. Run that same easy day at what feels like a respectable pace instead of an honestly easy one, and the heart rate follows it straight past 70% and into Zone 3: fast enough to accumulate fatigue, not fast enough to earn the adaptation Zone 5 work is designed for. Zone 3 is not a mistake anyone makes on purpose — it is what happens by default when “easy” gets defined by ego rather than by a number on a strap. Run your own recent times through the pace calculator to see where your usual “easy” actually sits.
What holding the zone actually buys you
The popular 80/20 approach puts roughly 80% of weekly training time in Zones 1–2 and 20% in Zones 3–5. It is not a rule for its own sake. It is what endurance training keeps landing on. In one study of national-level junior skiers, about 75% of sessions sat clearly below the first ventilatory threshold. In a nine-week trial with well-trained endurance athletes, a polarised mix of mostly easy work plus some hard sessions improved key endurance measures more than threshold, high-intensity or high-volume training did.
The aerobic base gets built by volume at a genuinely low intensity. The sharp end gets sharper by staying sharp, not by living in the tired middle. Skipping that discipline does not make a runner fitter faster. Every session ends up costing about the same in fatigue, easy and hard alike, which is the fastest route to a plateau a plan on paper cannot explain.
None of this needs a lab. Work out your zones once with the heart rate zones calculator, and find what that easy pace looks like on the road with the pace calculator. Then do the harder part: run slow enough, on purpose, on the days that are supposed to be slow.