# Circadian vs Project Function

The clearest difference is in-app purchases: Project Function at none against Circadian's 12. Project Function also leads on device support (4 vs 2). Circadian's advantage is iOS requirement (13.4 vs 15.5). On price, update cadence and ads there is nothing between them.

Both are free to download. Circadian sells 12 in-app purchases, starting at $1.99 per month. Project Function asks for nothing beyond the download.

Circadian ships an update every 3 weeks, Project Function every 6 weeks. The most recent releases landed on October 24, 2026 and October 9, 2026 respectively.

## The numbers

| Metric | Circadian | Project Function |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[4.6 (668 ratings)](https://appshunter.io/ios/app/circadian-your-natural-rhythm/id1495373007/reviews)** | — |
| Number of ratings | **668** | — |
| Positive reviews | 77.7% of reviews | — |
| In-app purchases | Yes | **No** |
| Ads | No | No |
| Update frequency | **Every 3 weeks** | Every 6 weeks |
| Monetization | Free with in-app purchases | — |
| Size | 67 MB | 181 MB |
| Requires iOS | **13.4** | 15.5 |
| Devices | iPhone, iPod | **iPhone, iPad, iPod, Apple Watch** |
| Age rating | 4+ | 4+ |
| Developer | [Circadian Limited](https://appshunter.io/developer/1495373006) | [Project Function LLC](https://appshunter.io/developer/1790112444) |

## What reviewers say

### Circadian

[App page](https://appshunter.io/ios/app/circadian-your-natural-rhythm/id1495373007)

Optimize your daily activities by syncing with natural rhythms. This app helps you wake, eat, move, work, and rest at optimal times for improved energy, clarity, and sleep. It leverages sunlight, seasons, and scientific principles to guide your lifestyle for better health.

**Highlights:** Sync daily activities to natural rhythms, Optimize wake, eat, move, work, and rest times, Align with sunlight and seasonal patterns, Seasonal sleep and meal timing calculator, In-app library on chronobiology and health, Set reminders for critical circadian events

**Features:** Family Sharing, Vision Pro support

**In-app purchases (12)**

| Purchase | Price | Billing |
| --- | --- | --- |
| 33% Off Monthly Subscription | $1.99 | per month |
| 10% Off Monthly Subscription | $2.49 | per month |
| Monthly Subscription | $2.99 | per month |
| 33% Off Yearly Subscription | $12.99 | per year |
| Circadian PLUS (yearly) 40% | $14.99 | per year |
| 10% Off Yearly Subscription | $17.99 | per year |
| Circadian PLUS (yearly) 25% | $18.99 | per year |
| Yearly Subscription | $19.99 | per year |
| Circadian PLUS (yearly) | $24.99 | per year |
| Circadian PRO (Lifetime) 40% | $47.99 | one-time |
| Lifetime Purchase - 33% Off | $49.99 | one-time |
| Circadian PRO (Lifetime) | $79.99 | one-time |

**What reviewers like**

- 👍 Easy to use
- 💡 Informative and educational
- 🚀 Helpful reminders and notifications
- 🌞 Supports circadian rhythm and natural lifestyle
- 🤩 Excellent customer service

**What reviewers complain about**

- 🐛 Crashes and bugs
- 🕰️ Inaccurate timing and location tracking
- 💰 Expensive subscription model
- 🤖 Rigid and inflexible scheduling
- 📱 Difficult to customize

**Reported bugs**

- Alarms not working properly
- Location and timezone issues
- Crashes and freezes during use
- Notifications not updating with changes

**Requested features**

- Customizable alarms and notifications
- Integration with other health/fitness apps
- Historical data tracking and trends
- Personalized recommendations based on user data
- Widget and Apple Watch support


### Project Function

[App page](https://appshunter.io/ios/app/project-function/id6740467390)

**Features:** Apple Wallet, Apple Watch app

**In-app purchases:** none


## Frequently asked questions

### Is Circadian free?

Circadian is free to download, with in-app purchases available.

### Is Project Function free?

Project Function is free to download, with no in-app purchases.

### Do Circadian or Project Function have ads?

Neither Circadian nor Project Function shows ads.

### Which is updated more often, Circadian or Project Function?

Circadian ships an update every 3 weeks, and Project Function every 6 weeks. Most recently, Circadian was updated on October 24, 2026 and Project Function on October 9, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*