To help drive home the privacy angle, you might consider open-sourcing it and also making it available on F-Droid. Also, why does it say "in-app purchases"? If this is a simple calendar I don't see why any purchasable extras should be necessary. (While many in the HN crowd lack the requisite equipment to make use of your project, we do have girlfriends, wives, sisters, and daughters who might benefit from a privacy-r…
The in-app purchases are a dealbreaker. Not only is there no reason for it, but it necessitates the integration of Google Play Services. If the goal was to be privacy-centric, it already fails at that for this alone. And if the goal was to profit off of women's need for privacy-centric period tracking, then there is absolutely no reason not to find a proper FOSS alternative that cares about its users more than making…
It could be an in-app purchase for themes or something like that. It can be a “thanks for supporting the app” cosmetic badge, completely optional, just there to buy a coffee for the author. But you’re dealbreaking it before you even see it?
In-app purchase != data collection
Also, regarding FOSS alternatives, you should know that FOSS does not mean “free from payment.” It technically doesn’t even mean “free from data collection.” It just means that the source code is available under a free and open source license. FOSS isn’t necessarily “free as in beer” and the FSF explicitly defines it that way. It’s more important that you’re offered the freedoms of the open source license and ability to get the source code. Whether or not you pay is a separate issue entirely.