Choosing a tracker
The best period tracker app: an honest guide to choosing one
The best period tracker app is the one that predicts sensibly from your own logged cycles, is clear about what it does with your data, lets you log the symptoms you care about and export your history for your GP, and is honest that it is not contraception unless it is approved as one. Quality varies a lot: in one review of free apps, only 20 of 108 met the researchers' accuracy and inclusion criteria.
Key facts
A 2016 evaluation of free menstrual tracking apps judged an app accurate if it predicted periods from at least three previous cycles, placed ovulation 13 to 15 days before the next period and contained no misinformation; 20 of the 108 apps assessed met the criteria. In 612,613 app-tracked cycles, the follicular phase varied far more than the luteal phase, which is why predictions from cycle length alone can be imprecise.
What makes the best period tracker app?
Search "best period tracker app" and you will find long lists, often written by the apps themselves. A better question is which app is best for what you want to do. Someone who only wants to know when her next period is due needs something different from someone tracking perimenopause symptoms, trying to understand premenstrual weight changes, or wanting to avoid pregnancy.
App quality is uneven. When researchers at Columbia University reviewed free menstrual tracking apps, they judged an app accurate if it predicted periods from an average of at least three previous cycles, placed ovulation 13 to 15 days before the next period and contained no misinformation. Of 108 apps that reached the final stage, only 20 met their criteria. Few cited medical literature or involved health professionals. That review is from 2016 and apps have changed since, but the checks it used are still good ones to apply yourself.
What to look for: a checklist
| What to check | What good looks like | Why it matters |
|---|---|---|
| Privacy and data use | A plain-English privacy policy that says whether your data is sold or shared, and an easy way to delete your account and data | Cycle data is sensitive health information |
| How it predicts | Predictions based on your own logged cycles, and it says how | Cycle length varies from month to month, especially before ovulation |
| Contraception claims | Clear about whether it is approved for contraception. Most trackers are not | A prediction is not protection |
| Symptom logging | Lets you log the symptoms you actually have, such as cramps, bloating, mood, sleep or hot flushes | Your own pattern is more useful than a generic chart |
| Export | Lets you export or share your history | The NHS suggests a symptom diary for at least two cycles to take to your GP |
| Cost | Clear pricing, and you know what the free version includes | Many apps charge for the features you want most |
| Fit with the rest of your health | Connects your cycle with what else you track, if you want that | Weight, sleep and energy all move with your cycle |
The same checks apply to cycle syncing, perimenopause and menopause apps.
How period predictions work, and their limits
Most trackers predict your next period from the length of your past cycles. That works reasonably well if your cycles are regular, but cycles vary. In more than 600,000 cycles logged in one app, the luteal phase (ovulation to period) averaged 12.4 days, while the follicular phase (period to ovulation) averaged 16.9 days and varied much more, from about 10 to 30 days. That is why the timing of ovulation, and so of your next period, is the hard part to predict from cycle length alone. The study's authors, who work for and were funded by the fertility app Natural Cycles, concluded that identifying fertile days needs physiological signs such as basal body temperature, not cycle length alone.
For most women, the practical point is simple: log every period, expect predictions to improve after a few cycles, and treat a predicted date as an estimate.
Period tracker apps and contraception
A period tracker that predicts a "fertile window" is not the same as contraception. Apple, for example, says its own Cycle Tracking feature should not be used as a form of birth control. Only rely on an app for contraception if it is specifically approved for that use, and talk to your GP or a sexual health clinic about which methods suit you.
When to see your GP: See your GP if your periods stop or change a lot, become very heavy or painful, or you bleed between periods or after sex. A tracker can show the pattern; it cannot tell you the cause.
Free period tracker options
If you mainly want dates and reminders, you may not need a separate app. On iPhone, the Health app has Cycle Tracking built in. According to Apple's Cycle Tracking guide, it predicts periods from the periods and cycle lengths you log, estimates a six-day fertile window with a calendar method, lets you log symptoms and export 12 months of cycle history as a PDF, and can flag patterns such as irregular or infrequent periods from your last six months of logs. Apple says that with two-factor authentication turned on, health data synced to iCloud is end-to-end encrypted so Apple cannot read it. If you use Android, check whether your phone or watch maker offers cycle tracking and read its privacy page.
Many standalone apps also have free versions. Use the checklist above, and read the privacy policy before you log anything.
Where Turtle fits
Turtle is not a dedicated period tracker, a fertility app or a contraceptive. It is a women's health coach with cycle tracking built in, and it suits a particular kind of woman: one who wants to understand how her cycle affects her weight, energy, sleep and training, alongside strength workouts, a food diary and a weekly check-in.
- Log your period and symptoms and see them next to your weight trend, sleep and training. See how to log a period and how to log cycle symptoms.
- Your period dates label your cycle context, so a premenstrual jump on the scale is read for what it is. Turtle uses them for context, not to diagnose anything.
- On iPhone, Turtle can read cycle data from Apple Health if you allow it, so you do not have to log twice. On Android, cycle import from Health Connect is not offered.
- Privacy: Turtle's privacy policy says it does not sell, rent or trade your personal information, and you can delete your account from inside the app.
- Cost: free to download, with membership at £14.99 a month or £39 a year.
Turtle is not the right choice if you want an app for contraception or for trying to conceive, or you only want free period dates. For those, a dedicated, approved app or your phone's built-in tracker will serve you better.
Try it yourself
Turtle: cycle tracking inside a women's health coach
Turtle is free to download, with membership at £14.99 a month or £39 a year. Log your period and symptoms and see them next to your weight, sleep and training.
4.6★ on the App Store · 100,000+ members · Free to download
How to choose in two minutes
- Only want dates and reminders? Try your phone's built-in tracker first.
- Want to avoid pregnancy? Talk to your GP or a sexual health clinic, and only use an app approved as contraception.
- Tracking perimenopause or PMS symptoms? Choose an app that lets you log those symptoms and export them.
- Want to understand your weight, energy and training across the month? Choose an app that puts your cycle next to those, such as Turtle.
New to the phases? Start with the menstrual cycle phases explained.
What the research says
Each study below was checked against its PubMed record, or read at source for NHS, NICE and government pages, on 7 October 2026.
A systematic evaluation of free smartphone menstrual tracking apps found that only 20 of 108 met the inclusion and accuracy criteria (predictions from at least three previous cycles, ovulation 13 to 15 days before the next period, no misinformation), and few cited medical literature or involved health professionals.
Moglia ML, Nguyen HV, Chyjek K, et al. (2016). Evaluation of Smartphone Menstrual Cycle Tracking Applications Using an Adapted APPLICATIONS Scoring System. Obstetrics and gynecology. 127(6):1153-1160 doi.org/10.1097/AOG.0000000000001444
In 612,613 cycles logged in the Natural Cycles app, the follicular phase averaged 16.9 days (range about 10 to 30) and the luteal phase 12.4 days (about 7 to 17). The authors said identifying fertile days needs physiological signs, not cycle length alone. The study was funded by Natural Cycles, and most authors work for or founded the company.
Bull JR, Rowland SP, Scherwitzl EB, et al. (2019). Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. NPJ digital medicine. 2:83 doi.org/10.1038/s41746-019-0152-7
The NHS says it is common for periods to come anywhere from every 21 to every 35 days, and that bleeding between periods or after sex needs to be checked by a doctor.
NHS. Periods. NHS website. Accessed 7 October 2026. www.nhs.uk/conditions/periods/
The NHS suggests keeping a diary of premenstrual symptoms for at least two menstrual cycles to take to a GP appointment.
NHS. PMS (premenstrual syndrome). NHS website. Accessed 7 October 2026. www.nhs.uk/conditions/pre-menstrual-syndrome/
Questions women ask
What is the most accurate period tracker app?
No app can know exactly when you will ovulate from cycle length alone. Look for one that predicts from your own logged cycles, explains how, and contains no misinformation. Predictions improve after a few cycles of logging.
Is there a free period tracker app?
Yes. iPhone has Cycle Tracking built into the Health app, and many standalone apps have free versions. Check what the free version includes and read the privacy policy.
Which period tracker app does not sell your data?
Read each app's privacy policy: it should say plainly whether data is sold or shared and how to delete it. Turtle's privacy policy says it does not sell, rent or trade personal information.
Can a period tracker app be used as contraception?
Only if it is specifically approved for contraception. Most period trackers are not, and Apple says its Cycle Tracking should not be used as birth control. Talk to your GP or a sexual health clinic.
Can I track perimenopause symptoms in a period tracker?
Many apps let you log symptoms such as hot flushes, sleep and mood. Choose one that lets you export your history so you can show your GP.
Is Turtle a period tracker?
Turtle is a women's health coach with cycle tracking built in. You can log your period and symptoms and see them alongside your weight, sleep and training. It is not a fertility or contraception app.
This guide is general information, not medical advice. It isn't tailored to you and doesn't replace advice from your GP or another qualified professional. If something's worrying you, speak to your GP. LeanShield™ is a trademark of ParrotPal Ltd: it rates the habits linked to protecting muscle, is not a medical device and doesn't measure muscle.