# Atomic Clock vs ThreeDay Calendar

The clearest difference is ads: Atomic Clock at none against ThreeDay Calendar's shown. ThreeDay Calendar's advantage is update cadence (fortnightly vs every 6 weeks). On price, in-app purchases, device support and iOS requirement there is nothing between them.

Both are free to download. Atomic Clock sells 2 in-app purchases, starting at $5.99 per month and ThreeDay Calendar sells 2 in-app purchases, starting at $0.99 per month. Whichever you choose, the download price is not the number that matters.

Atomic Clock ships an update every 6 weeks, ThreeDay Calendar fortnightly. The most recent releases landed on September 18, 2026 and August 23, 2026 respectively.

## The numbers

| Metric | Atomic Clock | ThreeDay Calendar |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[4.8 (4 ratings)](https://appshunter.io/ios/app/atomic-clock-precision-time/id6760377377/reviews)** | — |
| Number of ratings | **4** | — |
| Positive reviews | 100.0% of reviews | — |
| In-app purchases | Yes | Yes |
| Ads | **No** | Yes |
| Update frequency | Every 6 weeks | **Fortnightly** |
| Monetization | Free with in-app purchases | — |
| Size | 9 MB | 6 MB |
| Requires iOS | **17.6** | 18.0 |
| Devices | iPhone | **iPhone, iPad** |
| Age rating | 4+ | 4+ |
| Developer | [家宝 戴](https://appshunter.io/developer/1826395838) | [Hoein Song](https://appshunter.io/developer/6785738562) |

## What reviewers say

### Atomic Clock

[App page](https://appshunter.io/ios/app/atomic-clock-precision-time/id6760377377)

This utility provides highly accurate time synchronization using NTP, displaying precise time with millisecond detail. It allows comparison with network time, shows sync offset and latency, and offers various clock styles with customization options. It's designed for users needing a reliable, precise reference clock.

**Highlights:** NTP-based time synchronization, Millisecond time detail, Local time and UTC display, Device offset and network latency indicators, Automatic sync, Multiple clock styles, Customizable colors and night mode

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

**In-app purchases (2)**

| Purchase | Price | Billing |
| --- | --- | --- |
| AtomicClock Pro Monthly | $5.99 | per month |
| AtomicClock Pro Monthly | $19.99 | per year |


### ThreeDay Calendar

[App page](https://appshunter.io/ios/app/threeday-calendar/id6785738560)

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

**In-app purchases (2)**

| Purchase | Price | Billing |
| --- | --- | --- |
| ThreeDay Premium Monthly | $0.99 | per month |
| ThreeDay Premium Yearly | $9.99 | per year |


## Frequently asked questions

### Is Atomic Clock free?

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

### Is ThreeDay Calendar free?

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

### Do Atomic Clock or ThreeDay Calendar have ads?

ThreeDay Calendar shows ads; Atomic Clock does not.

### Which is updated more often, Atomic Clock or ThreeDay Calendar?

Atomic Clock ships an update every 6 weeks, and ThreeDay Calendar fortnightly. Most recently, Atomic Clock was updated on September 18, 2026 and ThreeDay Calendar on August 23, 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.*