An app can tell you which day of your cycle it is, by counting from the days you marked, and it can lay that calendar under your own training charts. It cannot tell you how you will feel, lift or weigh on any given day — and Zyra Workouts is built not to pretend otherwise. This article states the exact rule the app uses to estimate cycle day and phase, describes what the optional chart overlay shows, and is explicit about what it does not claim.
How the phase is estimated (the exact rule)
The app stores exactly one kind of cycle data: a set of calendar days you marked as period days, toggled on or off from the cycle screen. Nothing else — no symptoms, no notes, no temperatures. Everything you see is derived from that set by four short functions.
| Step | Rule (from the app's code) | Example |
|---|---|---|
| Period starts | A marked day whose previous day is not marked | Marked 3, 4, 5 May and 31 May, 1 June → starts on 3 May and 31 May |
| Cycle day | Days since the most recent start, counting the start as day 1 | On 10 June, with the last start on 31 May, cycle day = 11 |
| Cycle length | Median of the gaps between consecutive starts, clamped to 21–35; 28 if fewer than two starts | Gaps of 28, 30 and 27 days → median 28 |
| Phase label | Cycle day ≤ round(length / 2) → follicular; otherwise luteal | Length 28 → days 1–14 follicular, 15–28 luteal |
A few properties of that rule are worth knowing. It uses the median rather than the mean, so a single unusually long or short cycle does not move the estimate. The clamp means the app will never assume a cycle shorter than 21 or longer than 35 days, whatever the data says. And the phase boundary is nothing more than the halfway point of the estimated length: it is a calendar convention, chosen so the two halves are comparable in size, not a claim about where any physiological event falls for you.
The dashboard shows the result as a small CYCLE tile — "Day N" and a 28-day grid of marked days — and the cycle screen shows "Cycle day N", or "No cycle data" until you have marked something. The tile can be switched off with the period-tracking setting.
In plain terms: the app counts days between the dates you gave it and splits the count in half. That is the whole estimate.
What the overlay on your volume chart shows
The Insights screen carries an opt-in overlay. Under More there is a switch, "Show cycle phases on charts", off by default. When it is on and at least one period day is marked, the volume and sets chart tints each bar's period by phase — follicular in one tint, luteal in another — and shows a two-item legend beneath the chart. With the switch off, or with no days marked, the chart is plain.
What the overlay shows is your data, unchanged, on a shaded calendar:
- Working sets and volume per period with the phase bands behind the bars, so you can see whether your own logged training tends to differ between the two halves.
- Recent records (estimated one-rep maxes, rep PRs) with the same bands is in the design (spec §11.9) but not drawn by any screen as of this writing — that half is coming.
That is all it does. It does not rescale, adjust or annotate the numbers; it does not change your targets; it does not generate a message. It gives you two shaded halves and your own bars, and leaves the reading to you. If a pattern exists in your data it will be visible; if none exists, the bands will look like decoration — which is the honest outcome.
What it deliberately does not claim
Because the phase is a calendar estimate and the overlay is a background shade, the app makes none of the following claims, and this article does not either:
| The app does not… | Because… |
|---|---|
| Predict how strong, tired or motivated you will be on a given day | The estimate contains no information about you beyond dates |
| Change your program, loads, targets or rest by phase | Any such change would be a claim about your physiology it cannot support |
| Explain a weigh-in or a girth reading by phase | It shows the calendar next to the data; it does not attribute cause |
| Tell you where ovulation or any other event falls | The halfway split is a convention for comparable bands, nothing more |
| Turn the overlay on for you | Cycle data is personal; the tile can be hidden and the overlay is a switch that stays off until you turn it on |
If you want to act on what you see — reshuffle a heavy week, plan a deload, take a note — that is your call, or one to make with a coach. The point of putting your own training numbers on your own calendar is that you become the person with the evidence, rather than the app telling you what the evidence should say.
The short version
Zyra Workouts stores the days you mark, finds period starts, estimates cycle length as the median gap clamped to 21–35 days (28 by default), and labels the first half of the cycle follicular and the second luteal. An optional, off-by-default overlay shades those two bands behind the Insights volume and sets chart so you can compare your own training numbers by phase; the same bands on the records chart are coming. The app claims nothing about how any phase affects you; it shows your data on a calendar and stops there. Training guidance only — nutrition and training decisions around your cycle are yours and your coach's. Educational overview only — not medical advice.