# Retro 15C vs HP

The clearest difference is rating: HP at 5.0 against Retro 15C's 4.3. HP also leads on update cadence (every 11 days vs every 53 months) and review sentiment (100% vs 76%). Retro 15C's advantage is ratings volume (212 vs 5) and iOS requirement (8.0 vs 17.2). On price, ads, in-app purchases and monetization model there is nothing between them.

Both are free to download. Neither carries in-app purchases, so what you see is what you pay.

HP holds the better App Store score, 5.0 against 4.3. That said, the two scores are not equally well evidenced: Retro 15C has 212 ratings behind it against 5, so its average is the more settled of the two. Written reviews point the same way: 76% of Retro 15C's written reviews are positive against 100% of HP's.

Retro 15C ships an update every 53 months, HP every 11 days. The most recent releases landed on October 15, 2026 and October 8, 2026 respectively.

## The numbers

| Metric | Retro 15C | HP |
| --- | --- | --- |
| Price | Free | Free |
| Rating | [4.3 (212 ratings)](https://appshunter.io/ios/app/retro-15c/id583559000/reviews) | **[5.0 (5 ratings)](https://appshunter.io/ios/app/hp-35/id6738010641/reviews)** |
| Number of ratings | **212** | 5 |
| Positive reviews | 76.1% of reviews | **100.0% of reviews** |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | Every 53 months | **Every 11 days** |
| Monetization | Free | Free |
| Size | 5 MB | 2 MB |
| Requires iOS | **8.0** | 17.2 |
| Devices | **iPhone, iPod** | iPhone |
| Age rating | 4+ | 4+ |
| Developer | [Greg Hewgill](https://appshunter.io/developer/517923493) | [Enrique Haro](https://appshunter.io/developer/1778874870) |

## What reviewers say

### Retro 15C

[App page](https://appshunter.io/ios/app/retro-15c/id583559000)

This app emulates a classic RPN scientific calculator, offering advanced features like complex number arithmetic, matrix calculations, and programmability. It provides a functional and complex tool reminiscent of 1980s calculators.

**Highlights:** Complex number arithmetic, Matrix calculations, Numerical root finder, Numerical integration, Statistical functions, Programmable

**Features:** macOS Compatibility

**In-app purchases:** none

**What reviewers like**

- 🚀 Lightning-fast calculator
- 👍 Authentic look and feel of HP 15C
- 🚀 Faster than real HP 15C
- 👍 Excellent RPN emulation
- 👍 Familiar interface for HP 15C users

**What reviewers complain about**

- 🐛 Doesn't save settings, programs, or memory
- 🐛 No key press feedback or sound
- 🐛 Blinking display issue with large calculations
- 🐛 Bugs with HMS conversions
- 🐛 Can't close app on newer iPhones

**Reported bugs**

- Blinking display with large calculations
- Bugs with HMS conversions
- Inability to close app on newer iPhones
- Stopped working with iOS 14 updates

**Requested features**

- Add haptic feedback on key presses
- Implement continuous memory to save settings and programs
- Add portrait mode option
- Improve compatibility with newer iOS versions
- Add copy/paste functionality for stack and registers


### HP

[App page](https://appshunter.io/ios/app/hp-35/id6738010641)

Emulates classic Hewlett Packard RPN scientific calculators from the 1970s. Experience the original HP-35, HP-45, and HP-21 models on your iPhone.

**Highlights:** RPN calculator emulation, HP-35 model, HP-45 model, HP-21 model, Classic scientific calculator interface

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

**In-app purchases:** none


## Frequently asked questions

### Is Retro 15C free?

Retro 15C is free to download, with no in-app purchases.

### Is HP free?

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

### Which has better reviews, Retro 15C or HP?

HP is rated higher. Retro 15C averages 4.3 out of 5 from 212 ratings, while HP averages 5.0 from 5 ratings.

### Do Retro 15C or HP have ads?

Neither Retro 15C nor HP shows ads.

### Which is updated more often, Retro 15C or HP?

Retro 15C ships an update every 53 months, and HP every 11 days. Most recently, Retro 15C was updated on October 15, 2026 and HP on October 8, 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.*