iPhone Screenshots


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.

What’s New

Version 1.1

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!

Ratings and Reviews

4.2 out of 5
137 Ratings

137 Ratings

Cheapskate01 ,


Good news: This app is still supported. With no updates (until now) since its original release in 2012, combined with that horrible splash screen iOS 10 slapped on it, that the app was no longer supported, I was a bit worried about the future of what has been my favorite calculator app. With this update, that fear goes away.

The only flaw in this emulation is that the 15C emulator loses ALL data and programming if the app is exited by double-clicking the home key. I can think of NOTHING else wrong with this app.

I am a bit concerned that (one) the name is changed to "Retro 15C," something about iTunes not allowing the word "free" in the name of an app. And (two), I am disappointed by the removal of "HP" in the "HP 15C" logo at the top right of the calculator. Likely, another problem either with iTunes or HP itself. Not a big issue, but I did really like the appearance of the original app, which was pretty much a photograph of a real 15C.

ONE RECOMMENDATION, perhaps off-point, but the HP 15C was one of a pair of must-have calculators, the other being the HP 12C, essentially a financial version of the HP 15C. This would be the perfect complement of perhaps the two most useful and friendly calculators ever manufactured.

Even to this day, I have both calculators. I love this 15C emulation. Wish I had a decent 12C emulation.

Wraggj ,

Simply the best

I'm thrilled it has been updated to 64-bit and will continue to be the best for years to come. Long live RPN and the 15c.

Original review 2016 - I was a 15c user for many years. When it finally died a few years ago I learned how difficult it was to find an RPN calculator. I bought one, but always missed my 15c. Now I have it back. This app instantly became my calculator. It is way better than my real RPN calculator.

I'm not sure what, if anything, might be better about the paid 15c apps, but I have zero motivation to pay and find out.

baddog42 ,

Best calculator on my iPhone

I grew up using HP calculators. Used an HP-45 for many years, then got a 15C for work. Still works great. Only changed the batteries twice since I got it in 1984.

This little gem is absolutely wonderful to have on my phone. It gets used at work and home. RPN is so much faster and efficient for me. It's great to have a calculator like this with me all the time.

Thank you for updating it to work with the new iOS. I was wondering what l would do if it didn't work anymore.

App Privacy

The developer, Greg Hewgill, has not provided details about its privacy practices and handling of data to Apple.

No Details Provided

The developer will be required to provide privacy details when they submit their next app update.


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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