Your period data never leaves your phone.
Here's why we built it that way.
When I started building ZestyCoach, I had to make a decision that scared me. I'm going to explain exactly what I decided and why — because you deserve to know.
I'm one person building this
I'm 23. I'm building ZestyCoach alone. I'm learning as I go. And at some point while building the cycle tracking feature, I had a moment of genuine fear — because I realised I was asking women to hand over some of the most sensitive information that exists about their bodies.
Period data isn't just personal. In the current legal climate, it can be consequential. It can be subpoenaed. It can be used in ways none of us want to think about. I thought about that for a long time before I wrote a single line of code for this feature.
The decision
Everything related to your cycle stays on your device. Full stop.
We don't store your period data on our servers. We don't have access to it. We can't sell it, share it, or hand it over — because we genuinely don't have it.
This includes your period start date, flow intensity, duration, symptoms you log, your cycle profile type (whether you're tracking a regular cycle, an irregular one, perimenopause, or anything else), and your current phase. All of it lives locally on your phone.
What stays where
| Period start dateon device | Never transmitted. Stored locally only. |
| Flow & durationon device | Never transmitted. Stored locally only. |
| Symptoms loggedon device | Never transmitted. Stored locally only. |
| Cycle profile typeon device | Regular, irregular, perimenopause — never transmitted. |
| Recommendation feedbackopt-in only | If you choose to help us improve — anonymised, no cycle data attached. |
The trade-off I'm making
Storing everything locally means I learn less about how the app is working in the aggregate. I can't see patterns across users. I can't automatically tune recommendations based on data. That's a real cost — and I'm choosing to pay it, because I think your trust matters more than my analytics.
If you want to help us improve, there's an opt-in option to share anonymised, cycle-data-free signals — things like whether a recommendation felt right. That's it. Nothing identifying. Nothing sensitive. And it's off by default.
The science behind the recommendations
The recommendations ZestyCoach makes — on nutrition, training, recovery — are built on peer-reviewed research, primarily the work of Dr. Stacy Sims, whose research on female physiology and athletic performance is the most rigorous in this space. Every suggestion traces back to a source. That documentation exists and I'll be publishing more of it over time.
I'm not a doctor. ZestyCoach is not medical advice. But the foundation it's built on is science.
Why I'm telling you this
Because I think you should know. Because I'd want to know. And because the kind of app I want to build is one where the founder can look every user in the eye and explain every decision she made.
This is that explanation.
April 2026