# Circadian Rhythm & Sleep vs Stack

The clearest difference is iOS requirement: Circadian Rhythm & Sleep at 16.4 against Stack's 18.0. On price, update cadence, ads and in-app purchases there is nothing between them.

Both are free to download. Circadian Rhythm & Sleep sells 3 in-app purchases, starting at $4.99 per 7 days and Stack sells 2 in-app purchases, starting at $9.99 per 7 days. Whichever you choose, the download price is not the number that matters.

Circadian Rhythm & Sleep ships an update fortnightly, Stack every 2 weeks. The most recent releases landed on October 31, 2026 and October 28, 2026 respectively.

## The numbers

| Metric | Circadian Rhythm & Sleep | Stack |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[4.4 (8 ratings)](https://appshunter.io/ios/app/circadian-rhythm-and-sleep-arc/id6758214892/reviews)** | — |
| Number of ratings | **8** | — |
| Positive reviews | 75.0% of reviews | — |
| In-app purchases | Yes | Yes |
| Ads | No | No |
| Update frequency | **Fortnightly** | Every 2 weeks |
| Monetization | Freemium | — |
| Size | 70 MB | 106 MB |
| Requires iOS | **16.4** | 18.0 |
| Devices | iPhone, iPad | iPhone, iPad |
| Age rating | 4+ | 17+ |
| Developer | [Pritam Ghosh](https://appshunter.io/developer/1871515469) | [Amari Thomas](https://appshunter.io/developer/1868315587) |

## What reviewers say

### Circadian Rhythm & Sleep

[App page](https://appshunter.io/ios/app/circadian-rhythm-and-sleep-arc/id6758214892)

This app analyzes your personal energy patterns to create a customized daily plan. It helps you understand your body's natural rhythms for optimal energy, focus, and well-being. Features include personalized caffeine cutoff times and adaptive daily adjustments.

**Highlights:** Personalized daily energy plan, Calculated caffeine cutoff times, Adaptive daily adjustments, Energy dip tracking and analysis, Short-term habit experiments, Educational briefings on sleep and timing

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases (3)**

| Purchase | Price | Billing |
| --- | --- | --- |
| ARC Weekly Pro | $4.99 | per 7 days |
| ARC Monthly Pro | $12.99 | per month |
| ARC Yearly Pro | $49.99 | per year |


### Stack

[App page](https://appshunter.io/ios/app/stack-peptide-tracker/id6773488687)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases (2)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Stack Weekly | $9.99 | per 7 days |
| Stack Yearly | $49.99 | per year |


## Frequently asked questions

### Is Circadian Rhythm & Sleep free?

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

### Is Stack free?

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

### Do Circadian Rhythm & Sleep or Stack have ads?

Neither Circadian Rhythm & Sleep nor Stack shows ads.

### Which is updated more often, Circadian Rhythm & Sleep or Stack?

Circadian Rhythm & Sleep ships an update fortnightly, and Stack every 2 weeks. Most recently, Circadian Rhythm & Sleep was updated on October 31, 2026 and Stack on October 28, 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.*