About Veil
A period & cycle tracker that believes your health data belongs to one person: you.
A cycle log is not just a cycle log.
Period tracking generates one of the most sensitive datasets you'll ever produce. In some places it can become evidence in a court case. In others it's a leverage point during a custody dispute, an immigration interview, or a divorce. Even where the legal stakes are zero, a breach is forever - data once leaked cannot be unleaked, and apologies do not unindex it from search engines.
Veil exists so you don't have to choose between knowing your body and being safe. The discreet mode, app lock, and on-device-only architecture were not bullet points - they were the brief.
Our mission
Veil exists because we believe cycle tracking should not require sending your most intimate health data to a remote server. Many period-tracking apps store your menstrual dates, symptoms, moods, and sexual activity in the cloud - sometimes for product improvement, sometimes for research, and sometimes in ways users may not fully expect. Even well-intentioned data collection creates risk: servers can be breached, policies can change, and data once collected is difficult to truly delete.
We built Veil to prove that a cycle tracker can be beautiful, smart, and research-informed without ever seeing your data. Every calculation runs on your phone. Every prediction is derived from your history alone. There are no accounts, no servers storing health data, and no way for us - or anyone else - to access what you log.
Our mission is simple: give people the best possible cycle-tracking experience with zero privacy compromises.
Local-first. Encrypted by default.
Everything you log stays on your device and nowhere else. There is no cloud, no server, and no way for us to see your data - because we never receive it in the first place.
Backups are encrypted with a password only you know. Your app lock PIN is securely hashed and stored in your phone's protected keychain. Even if someone gets the backup file, they cannot read it without your password.
Our vision
We envision a world where health apps respect their users by default - where privacy is not a premium feature or an opt-in setting, but the foundation everything is built on.
Veil is available in 9 languages, works in discreet mode for users who need discretion, and offers biometric + PIN app lock for those in sensitive situations. We believe privacy is not just about data - it is about safety, autonomy, and dignity.
How predictions work
Some cycle-tracking apps use cloud-based machine-learning models trained on aggregated user data to generate predictions. Veil takes a fundamentally different approach: your predictions are powered entirely by your own logged history. No population-level data, no shared models, no one else's cycles influencing your forecast.
Veil uses an exponentially weighted moving average (EWMA) across your most recent cycles, with automatic outlier exclusion so a single stress or illness cycle does not throw off the model. The more cycles you log, the more accurate your predictions become. After 3-4 complete cycles, most users see predictions landing within 1-3 days of their actual period start.
Fertile-window and ovulation predictions follow the established medical evidence: a 7-day window modeled on the landmark Wilcox et al. (1995) study, extended by one day to account for the inherent uncertainty of cycle-math prediction (as opposed to hormone-confirmed ovulation). Users who track basal body temperature and cervical mucus can also get symptothermal ovulation confirmation using the Sensiplan 3-over-6 BBT rule.
The more you log, the better it gets.
Veil learns exclusively from your own data. Every symptom, mood, energy level, sleep entry, and pill log you add gives the prediction engine more signal to work with. There is no shortcut - and no cloud model can substitute for your personal cycle history.
Medical grounding
Every clinical threshold, score, and detection rule in Veil is grounded in published medical literature. We do not guess numbers or invent scales. Key references include:
- PMDD severity score - weighted per the 11 DSM-5 criteria for premenstrual dysphoric disorder, with sleep thresholds from AASM/SRS consensus and DSM-5-TR hypersomnolence criteria.
- Cycle regularity - classified per FIGO 2018 age-banded thresholds (Munro et al.).
- Amenorrhea detection - follows ACOG, AAFP, and ASRM 2024 definitions for secondary amenorrhea (90 days for regular cycles, 180 for irregular).
- Oral-contraceptive detection - aligned with the CDC/ACOG 7-day rule for ovulation suppression.
- Symptothermal ovulation - Sensiplan 3-over-6 BBT rule (Frank-Herrmann et al., 2007) and Billings peak-mucus confirmation.
- Fertile window - based on Wilcox et al. (NEJM 1995), extended per Dunson/Baird/Wilcox (1999) measurement-error model.
Medical disclaimer
Veil is a self-tracking aid, not a medical device. It is not intended to diagnose, treat, cure, or prevent any disease or medical condition. Cycle predictions, PMDD severity scores, health alerts, symptothermal ovulation detection, oral-contraceptive mode, and amenorrhea flags are based on the data you personally enter and are provided for informational and self-tracking purposes only.
All calculations and predictions are derived from established medical textbooks, peer-reviewed research, and clinical guidelines (ACOG, FIGO, WHO, CDC, AASM, DSM-5). However, they are not a substitute for professional medical advice, diagnosis, or treatment. Individual physiology varies, and no algorithm - no matter how well-cited - can replace a clinician's judgment.
Predictions are computed entirely from your own locally stored data. Veil does not use population-level machine-learning models, does not train on other users' data, and does not upload your health information to any server. This means predictions improve as you log more data - not as other people do.
Veil should not be used as a method of contraception or fertility planning. If you have concerns about your menstrual health, experience prolonged changes in your cycle, or notice symptoms that affect your daily life, please consult a qualified healthcare provider.
Get in touch
Questions or feedback? Reach us at feedback@veiltrack.app . We read every message.
Third-party attribution
- Contraception icons by Health Icons - MIT License.