Flo is the most downloaded period tracker on the planet, with hundreds of millions of users and a polished product. People look for a Flo alternative for a few recurring reasons: the paywall, the ads in the free tier, or the privacy history. Here's an honest breakdown of how Crimson compares, based on publicly available information from both apps.
Crimson vs Flo: the quick comparison
| Feature | Crimson | Flo |
|---|---|---|
| Price | Free tier + optional Pro (14-day trial) | Free tier + Premium at $49.99/yr |
| AI Assistant | Included, works out of the box; unlimited with Pro | Limited, Premium only |
| Ads in Free Tier | No ads | Yes |
| Account Required | Yes (secure sign-in via Clerk) | Yes |
| Data Encryption | Encrypted in transit (TLS 1.2+) & at rest | Encrypted at rest |
| Health Data Sold or Shared | Never | 2021 FTC settlement over past sharing |
| Symptom Tracking | 70+ symptoms | 50+ symptoms |
| Modes | Cycle, TTC, pregnancy, perimenopause | Cycle, TTC, pregnancy, perimenopause |
| Reports for Your Doctor | Free PDF reports + CSV export with date filtering | Health reports, Premium only |
| Platforms | iOS, Android | iOS, Android, Web |
Where Flo wins
Credit where it's due. Flo has the largest user base in the category, which means a massive community and years of prediction tuning. Its health content library is extensive and reviewed by a large medical team, and it offers a web app so you can check your cycle from a browser. If you want the biggest, most established app with the most reading material, Flo is a reasonable pick. You can check their current features at flo.health.
Where Crimson wins
- A free tier that's actually useful. Logging, predictions, all four modes, 70+ symptoms, a daily AI allowance, and CSV/PDF exports. No ads. Crimson Pro exists for one thing: unlimited AI.
- AI that works out of the box. No API key, no setup, no Premium gate to start. The assistant knows your current cycle phase and recent symptoms, so answers fit where you actually are in your cycle.
- Dedicated perimenopause mode. Hot-flash tracking with triggers, hormone result logging, and patterns built for this stage, not a bolted-on article section.
- Privacy without the history. Crimson has never sold or shared health data with advertisers, period. Details on our private period tracker page and in the privacy policy.
The privacy question
This is the difference most switchers care about. In 2021, the FTC finalized a settlement with Flo after alleging the app shared users' sensitive health data with third parties, including Facebook and Google, between 2016 and 2019, despite privacy promises to the contrary. You can read the FTC's announcement yourself. Flo says it has overhauled its practices since, and it now offers an Anonymous Mode.
Crimson's model is simpler: local-first storage, sync encrypted in transit and at rest, and a business that doesn't touch advertising. We require an account (handled by Clerk) so your synced data sits behind proper authentication. One honest caveat: we don't offer end-to-end encryption, and we won't pretend otherwise.
The bottom line
Stick with Flo if you want the biggest community, the deepest content library, and a web app, and you're comfortable with Premium pricing for the good stuff.
Try Crimson if you want a Flo alternative with a free tier that does real work, AI that knows your cycle out of the box, a true perimenopause mode, and a privacy record with no asterisks. Want the full field? See our five-app comparison, or learn the cycle basics in the guide.
Prices and features verified July 2026. Sources: Flo's official site and the FTC's 2021 Flo Health order. Flo features may change; check their listing for the latest.
Frequently asked questions
Is Crimson a good Flo alternative?
It depends on what you're switching for. If you want a privacy-first tracker with a genuinely useful free tier, an AI assistant that works out of the box, and a dedicated perimenopause mode, Crimson is built for exactly that. If you want the largest community, a big library of expert-reviewed health content, and a web app, Flo still does those things better. Both apps cover period, fertility, and pregnancy tracking on iOS and Android.
Is Flo private?
Flo encrypts user data and says it does not sell personal information. However, in 2021 the FTC finalized a settlement with Flo after alleging the app shared users' health data with third parties including Facebook and Google between 2016 and 2019, contrary to its privacy promises. Flo has since updated its practices and added an Anonymous Mode. Whether that's enough is a personal call; reading any app's current privacy policy is the best check.
Is Crimson free compared to Flo Premium?
Crimson's free tier covers logging, predictions, all four modes, 70+ symptoms, a daily AI allowance, and free CSV and PDF exports. New accounts start with a 14-day trial of Crimson Pro, which adds unlimited AI. Flo also has a free tier, but many of its insights, reports, and AI features sit behind Flo Premium, listed at $49.99 per year as of July 2026.
Can I move my data from Flo to Crimson?
There's no automatic import between the two apps. The practical path most people take: log your last period start date and typical cycle length when you set up Crimson, and predictions recalibrate as you log new cycles. Predictions get sharper within a couple of months of consistent logging.
Try the privacy-first alternative
Free tier with a 14-day Pro trial. AI that knows your cycle, out of the box. Your data never for sale.