How Helix reads your numbers.

Your own normal

Every number in Helix is read against your own rolling 30-day baseline — never a population average. A resting heart rate of 58 means one thing for a cyclist whose normal is 46, and something else entirely for someone whose normal is 64.

When you first open Helix it reads up to 90 days of history from Apple Health, on your phone, so your baselines exist from the first morning. After that they move with you: a block of good training shifts your normal, and Helix follows.

A baseline is more than an average. Helix also tracks how much each signal usually varies for you, so a change is judged against your own day-to-day noise. A 5 ms dip in HRV can be nothing for one person and a clear signal for another.

How Readiness is made

Readiness is one score each morning, from 0 to 100, built from systems rather than single numbers:

• Autonomic — heart rate variability, resting heart rate and the overnight markers (respiratory rate, wrist temperature where your device records them).
• Sleep — how much you slept against what you needed, and how well the night held together.
• Training load — the strain of recent days against what you’re used to.

Each system is compared with your baseline, then weighted. On a typical morning the autonomic system carries the most weight, because it responds first when your body is under strain. The weights shown in the app are the ones used that morning, not a fixed formula.

What today’s score stands on

Below the score, Helix lists every input it used: whether it was measured, carried, estimated or reported, and how much it counted. If you want to know why you’re a 40 today, the answer is one tap away.

Missing signals and ranges

Devices miss things: a watch left on the charger, a ring that slipped, a night with no HRV reading. Helix never quietly fills the gap and presents the result as certain.

• When a signal is missing, the score says so, and shows a likely range instead of pretending to be exact.
• The more that’s missing, the wider the range.
• A last good reading may be carried forward for a short time, and is labelled as carried.

No HRV? The morning check-in

Not every device passes heart rate variability to Apple Health. When HRV isn’t available, resting heart rate and sleep carry more of the score, each still against your own baseline, and the app shows that the fallback is in use.

The Morning check-in fills in the rest: four questions in thirty seconds — how you slept, how your body feels, your energy and your mood. It also helps on days your device did record everything, because how you feel is a signal in its own right.

Strain, fitness, form and ramp

• Day strain — how hard the day was on your cardiovascular system, from heart rate during sessions and across the day.
• Fitness — the load you’ve been absorbing over recent weeks.
• Form — fitness minus recent fatigue. Negative while you’re building; positive when you’re fresh.
• Ramp — how fast fitness is rising. A steep ramp is the most common route to illness and injury, so Helix flags it.

Sessions without heart rate are estimated from how hard you rated them. Sessions with heart rate are measured.

How it all connects

Helix looks for relationships in your own data — late meals and sleep, hard days and next-morning HRV — and tests each one for statistical significance before showing it. If there isn’t enough data to say, it says that instead.

Not a diagnosis

Helix is not a medical device. It does not diagnose, treat or prevent any condition. Its scores are estimates from consumer devices and can be wrong. The Early-warning card says when several overnight markers move together; it can’t tell you why. If you feel unwell, or are worried about a reading, speak to a GP or call NHS 111. In an emergency, call 999.