I wrote a period app for my partner, everything is encrypted and never leaves the device.

It has a option where you can set false passwords, so that if you are being compelled to unlock it, it will get up fake data.

Code is open source: https://github.com/cameroncros/PrivatePeriodTracker

https://play.google.com/store/apps/details?id=com.cross.privateperiodtracker

It may not meet your needs, but perhaps worth a look. I am open to adding features (except for ads and tracking obviously).

(I have posted this before, but with an inappropriate account)

Got nothing to suggest but just wanted to call out that you're an awesome dad parent.

Sorry, I'm just a dude with no periods that buries my head in the sand a bit to much. The government is doing fucking WHAT with your period information? How is this any of their business? Why would they want to know this information?

Menstrual cycle trackers

• Drip - Menstrual cycle and fertility tracking. Everything you enter stays on your device.
• log28 - a (very) simple no-frills period tracker for Android.

Use the one built into iPhones and either encrypt iCloud so Apple cannot read it ( but no way to recover if you forget password) or turn off iCloud sync for health data (you will lose history with new phone).

Or, print out a one page annual calendar and use a pencil.

F-droid has a few Android apps: https://search.f-droid.org/?q=period&lang=en

Edit: this one also seems to work on iOS: https://bloodyhealth.gitlab.io/

A woman. I'm interested too... It's really tiring keeping track of it on an analog Calendar.

If you can't find anything, I suggest you make her a barebones one or get her to use something like etar. It's all local.

Drip is a good option. Funded by Mozilla and German Govt

Look into Periodical as well, it's on fdroid and completely local. It also shows when the next period should be and works better than some closed source apps.

I'd probably just spin up a calendar such as one on Nextcloud but also change the name of the event to another plausible name such as:

Pay day.
Grandma coming to town.
Grandma leaving town.
Walk the cat.
Pick up groceries.
Collect mail.
Drop off mail.

Drip is one of the better options if you want to just download something from your app store of choice. It’s FOSS, requires minimal permissions, and seems to store all data locally.

I'm looking for a good option too. Hopefully someone chimes in with something!