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Bluemoon vs Periodical: catalog facts
Bluemoon	Periodical
Best for: People who want a private, simple period tracker on Android	Best for: Android users who want a private, open-source period calendar
Free Free and open source.	Free Free and open source under the GPL-3.0-or-later licence.
Android	Android
Data stays on the device Simple interface All 3 strengths for Bluemoon Data stays on the device Simple interface Available on F-Droid and Google Play	Calculates fertile days and tracks symptoms and notes Backup to a single compressed file on local storage All 4 strengths for Periodical Calculates fertile days and tracks symptoms and notes Backup to a single compressed file on local storage Available from F-Droid, Google Play or as an APK Translated through a community Crowdin project
Android only Focused on basic tracking rather than detailed health insights	Calendar method is not reliable for contraception Simple feature set compared with commercial cycle trackers
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0-or-later	License: GPL-3.0-or-later
No account needed	Not stated if an account is needed
Offline features available	Not stated if it works offline
Official website Full listing and sources Sources for Bluemoon nilsgrob.ch/work/bluemoon Catalog checked October 2, 2026	Official website Full listing and sources Sources for Periodical arnowelzel.de/projekte/periodical f-droid.org/packages/de.arnowelzel.android.periodical Catalog checked October 2, 2026

“Not stated” means we have not confirmed it. Features can vary by device and plan.