# Decay calc vs Rail Model Calc

The clearest difference is in-app purchases: Rail Model Calc at none against Decay calc's 1. Decay calc's advantage is ads (none vs shown) and update cadence (every 3 months vs every 14 months). On price, device support and iOS requirement there is nothing between them.

Both are free to download. Decay calc sells 1 one-off in-app purchase. Rail Model Calc asks for nothing beyond the download.

Decay calc ships an update every 3 months, Rail Model Calc every 14 months. The most recent releases landed on October 8, 2026 and October 1, 2026 respectively.

## The numbers

| Metric | Decay calc | Rail Model Calc |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[1.0 (1 ratings)](https://appshunter.io/ios/app/decay-calc/id1479526735/reviews)** | — |
| Number of ratings | **1** | — |
| Positive reviews | 50.0% of reviews | — |
| In-app purchases | Yes | **No** |
| Ads | **No** | Yes |
| Update frequency | **Every 3 months** | Every 14 months |
| Monetization | Free with in-app purchases | — |
| Size | 27 MB | 13 MB |
| Requires iOS | **15.2** | 15.4 |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 17+ | 4+ |
| Developer | [Alexey Baranov](https://appshunter.io/developer/1479526734) | [Nobuyuki Kumakura](https://appshunter.io/developer/1529070760) |

## What reviewers say

### Decay calc

[App page](https://appshunter.io/ios/app/decay-calc/id1479526735)

This tool calculates the decay of radioactive isotopes over time, considering half-life for accurate activity predictions. It's useful in nuclear medicine, environmental monitoring, and radiation safety for handling and disposal of materials.

**Highlights:** Radioactive isotope decay calculation, Half-life integration, Activity prediction, Decay constant determination, Radiation dose calculation

**Features:** macOS Compatibility

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Radio calc | $0.99 | one-time |


### Rail Model Calc

[App page](https://appshunter.io/ios/app/rail-model-calc/id6474500872)

**Features:** macOS Compatibility

**In-app purchases:** none


## Frequently asked questions

### Is Decay calc free?

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

### Is Rail Model Calc free?

Rail Model Calc is free to download, with no in-app purchases.

### Do Decay calc or Rail Model Calc have ads?

Rail Model Calc shows ads; Decay calc does not.

### Which is updated more often, Decay calc or Rail Model Calc?

Decay calc ships an update every 3 months, and Rail Model Calc every 14 months. Most recently, Decay calc was updated on October 8, 2026 and Rail Model Calc on October 1, 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.*