Natural Cycles
Natural Cycles — Cycle & Fertility Tracker
7.5/10 overallAround £90/year subscription (thermometer often included)
A temperature-based cycle tracking app that's been through formal clinical validation studies, paired with a basal thermometer.
The verdict
Natural Cycles combines daily basal temperature readings with cycle data in an algorithm that's been through published clinical validation studies, at around £90/year with a thermometer often included. It's best for those who want an evidence-backed app rather than pure prediction and are willing to test consistently — the subscription-only pricing makes it a harder sell than free apps.
Natural Cycles differs from Flo's app already in this category in one specific way: its algorithm has been through published clinical validation studies for both contraceptive and conception use, giving it a stronger evidence basis than most cycle-tracking apps, which typically rely on prediction rather than validated algorithms. It works by combining daily basal temperature readings (via a paired or compatible thermometer) with your cycle data, rather than predicting from calendar data alone.
Against Femometer's standalone Vinca thermometer also in this category, Natural Cycles is the fuller ecosystem — app subscription plus thermometer — versus a standalone hardware device you could pair with any tracking method. The subscription cost is the main trade-off: unlike Flo's free tier, Natural Cycles is subscription-only, reflecting its clinically-validated positioning.
Is the Natural Cycles — Cycle & Fertility Tracker worth it?
- Clinically validated algorithm, stronger evidence base than most tracking apps
- Combines temperature data with cycle prediction for greater accuracy
- Reputable for both conception and contraceptive use cases
What are the downsides of the Natural Cycles — Cycle & Fertility Tracker?
- Subscription-only, no free tier
- Requires consistent daily temperature readings to work well
- Pricier overall than free apps paired with a separate basic thermometer
Specs
- Hardware
- Bundled or compatible basal thermometer
- Platform
- iOS and Android
- Free tier
- No, subscription only
- Tracking method
- Basal temperature + cycle data algorithm
- Clinical validation
- Yes, published studies
How we scored it
Prediction Accuracy
How reliably the tool identifies or confirms the fertile window.
Clinically validated algorithm gives stronger evidence-backed accuracy than prediction-only apps.
Ease of Daily Use
How simple it is to fit into a daily routine.
Requires consistent daily temperature discipline, more effort than calendar-only apps.
Value for Money
Subscription or purchase cost relative to what you get.
Subscription-only pricing is higher than free-tier competitors.
Weighted by importance for this category — see our editorial policy for how we test.
How this review was done
We haven't used the Natural Cycles — Cycle & Fertility Tracker ourselves yet. This review is built from Natural Cycles's published specifications and product information, and scored the same way as everything else on the site. We'll update it, and the badge above, once we've tested it hands-on.
How it compares
|  |  |  | |
|---|---|---|---|---|
| Price | Around £90/year subscription (thermometer often included) | Around £249 one-off for the bracelet | Around £200 for the analyser (wands sold separately) | £64.99 (monitor + 10 test sticks), refills from £29.99 |
| Overall score | 7.5/10 | 7.7/10 | 6.9/10 | 7.1/10 |
| Tracking method | Basal temperature + cycle data algorithm | Multi-signal overnight wearable (temperature, pulse, breathing) | Quantified LH/estrogen hormone analysis | — |
| Format | — | Wrist-worn bracelet + companion app | Analyser device + disposable test wands | — |
Frequently asked questions
Is Natural Cycles clinically validated?+
Yes — unlike most cycle-tracking apps, which rely on prediction from calendar data, Natural Cycles' algorithm has been through published clinical validation studies for both contraceptive and conception use, giving it a stronger evidence basis.
Does Natural Cycles need a separate thermometer?+
It works by combining daily basal temperature readings, via a bundled or compatible thermometer, with your cycle data rather than predicting from calendar averages alone. The thermometer is often included in the subscription price.
Is there a free version of Natural Cycles?+
No — unlike Flo, which has a free tier for basic logging, Natural Cycles is subscription-only, reflecting its clinically-validated positioning.
Do I need to test at the same time every day with Natural Cycles?+
Yes, it requires consistent daily temperature readings to work well, similar to any basal-temperature-based method — inconsistent testing will undermine the accuracy of its predictions.
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Reviewed by
Sepehr
Software engineer, soon-to-be dad, uncle to four — the tech-obsessed half of the two of us testing this stuff. Currently building this site with my wife, ahead of our own baby arriving.