# Retro 15C

> Free RPN scientific calculator with complex math, matrices, and programming. (iPhone/iPad app by Greg Hewgill.)

- Source: https://appshunter.io/ios/app/retro-15c/id583559000 (this page in markdown: same URL + `.md`)
- Developer: [Greg Hewgill](https://appshunter.io/developer/517923493)
- Category: Utilities, Education
- Price: Free
- Rating: 4.30/5 from 212 App Store ratings · 113 written reviews indexed
- Age rating: 4+
- Requires: iOS 8.0 · 5 MB
- Languages: American English
- Released: 2012-12-15
- Data updated: 2026-07-10
- Monetization: free
- User reviews in markdown: https://appshunter.io/ios/app/retro-15c/id583559000/reviews.md

## What is Retro 15C?

Students and scientists from the 1980s will remember the classic RPN scientific calculators. These calculators strike a perfect balance between functionality and complexity.

* Complex number arithmetic and trig functions
* Matrix calculations
* Numerical root finder
* Numerical integration
* Statistical functions, linear regression
* Fully programmable

This app is completely free, no ads or extra bits to buy. I love this calculator and I like to share.

## Key features

- Complex number arithmetic
- Matrix calculations
- Numerical root finder
- Numerical integration
- Statistical functions
- Programmable

## What do users think of Retro 15C?

Overall sentiment: positive

**Pros**

- 🚀 Lightning-fast calculator
- 👍 Authentic look and feel of HP 15C
- 🚀 Faster than real HP 15C
- 👍 Excellent RPN emulation
- 👍 Familiar interface for HP 15C users
- 👍 Great representation of original calculator
- 👍 Obvious labor of love by developer

**Cons**

- 🐛 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

**Commonly reported bugs**

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

**Most 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

## Recent user reviews (10 of 113)

All indexed reviews: https://appshunter.io/ios/app/retro-15c/id583559000/reviews.md

### 5/5 — Outstanding program

*2026-06-23, version 1.1*

The designers/coders sweat the details. The appearance of the calculator is identical to the physical calculator.  Excellent work !!!

### 4/5 — iPhone 17

*2026-03-17, version 1.1*

It’s apparently not possible to close the screen, or close the app on the iPhone 27, which has virtual handles on the screen corners. You must turn off the screen and then switch. Thanks for your support. 
I hope you can fix this, as I have enjoyed the app for many years.

### 1/5 — Bad app

*2025-11-04, version 1.1*

Locks my iPhone in landscape mode, next to impossible to exit app

### 5/5 — An old friend

*2025-09-05, version 1.1*

I was delighted to find this.  I still own, and use, both 40 year old 15C and 12C calculators I acquired working at the HP IC fab that made chips for them.  Thanks for bringing the 15C to my iPhone!

### 3/5 — Good, but no way out

*2025-08-25, version 1.1*

As far as a HP11, it’s fine. But, there is no exit button, half swipe up app switcher fails also

### 5/5 — Just the best thing!

*2025-02-06, version 1.1*

Appreciate the work to keep the app current.

### 5/5 — Engineering must

*2024-10-31, version 1.1*

I’ve been using this for many years in my work. Love it. Except, this week, the entire screen started to blink. Is there a fix?

### 5/5 — Fantastic

*2024-10-05, version 1.1*

If you know, you know…

### 5/5 — An Old Friend now on my phone

*2024-09-16, version 1.1*

Near perfection.  The only thing I wish they would do is to add haptic feedback on the keyboard.  Well done , guys.

### 5/5 — Still working on iOS 18

*2024-09-16, version 1.1*

Just like the original calculator that I used as I got my PhD in physics. The best by HP.

## Frequently asked questions about Retro 15C

### What does the Retro 15C app do?

The Retro 15C app emulates a classic RPN (Reverse Polish Notation) scientific calculator. It offers a wide range of advanced mathematical functions, including complex number arithmetic, matrix calculations, numerical root finding, and integration.

### What are the key features of this calculator app?

Key features include complex number arithmetic and trig functions, matrix calculations, a numerical root finder, numerical integration, statistical functions with linear regression, and full programmability. It aims to replicate the functionality of classic 1980s RPN calculators.

### Is this app free to use?

Yes, the Retro 15C app is completely free to use. The developer has stated there are no ads or extra in-app purchases, making it a free offering.

### Who is the target audience for this app?

This app is designed for students and scientists who remember or appreciate the functionality of classic RPN scientific calculators from the 1980s. It appeals to users who value a balance between functionality and complexity in their calculation tools.

## Version history (last 2 releases)

### 1.1 — 2017-04-27

This app has been updated by Apple to display the Apple Watch app icon.

Updated 64 bit build that will survive long past the next iOS update. 

Also, the calculator display now scales correctly for all iPhone screen sizes.

The name of the app has been changed to "Retro 15C". It's still free and always will be.

Thank you for your support!

### 1.0 — 2012-12-15

No release notes.

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## More apps by Greg Hewgill

- [Auckland Trains](https://appshunter.io/ios/app/auckland-trains/id530757295)
- [Simon Tatham's Puzzles](https://appshunter.io/ios/app/simon-tathams-puzzles/id622220631)

All apps by Greg Hewgill: https://appshunter.io/developer/517923493

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-07-10.*