# Janus Calculator

> Dual-notation programmable calculator with finance, scientific, and option functions. (iPhone/iPad app by Geoffrey Domm.)

- Source: https://appshunter.io/ios/app/janus-calculator/id373378721 (this page in markdown: same URL + `.md`)
- Developer: [Geoffrey Domm](https://appshunter.io/developer/373378724)
- Category: Productivity, Finance
- Price: Free
- Rating: 2.00/5 from 1 App Store ratings · 6 written reviews indexed
- Age rating: 4+
- Requires: iOS 26.2 · 1 MB
- Languages: English
- Released: 2010-05-26
- Data updated: 2026-06-03
- Monetization: free
- User reviews in markdown: https://appshunter.io/ios/app/janus-calculator/id373378721/reviews.md

## What is Janus Calculator?

Two-sided calculator.  Side A uses Standard Notation, Side B uses Reverse Polish Notation.  Both calculators are programmable, include various finance and scientific functions, and the values of 45 physical constants.  Also includes a Black-Scholes option calculator, including calculation of implied values for each of the inputs.

## Key features

- Dual calculator interface (Standard and RPN)
- Programmable functions
- Finance and scientific functions
- Physical constants
- Black-Scholes option calculator
- Implied value calculation

## Recent user reviews (6 of 6)

All indexed reviews: https://appshunter.io/ios/app/janus-calculator/id373378721/reviews.md

### 4/5 — A neat LITTLE thing

*2020-04-25*

Took me a while to discover the RPN calculator because as usual, I open my iPad in Landscape orientation - which does not provide any information or flip button until you go into portrait view. In portrait, one can access the info button and choose the RPN calculator; and one's preferences are retained when reverting to landscape.

It functions well but is very small on my screen regardless of orientation. The useful key click is selectable as ON or OFF but when ON, is very load, requiring volume adjustment of the of the device.

But the bottom line is that it functions properly; it's free; and it has no distractive advertising or pop-up prompts for reviews or upgrading.
So, thankyou, Geoffrey: I'm keeping it. [Just wish it were bigger…] ;-)

### 3/5 — Correction to previous review

*2017-12-16*

The Janus Calculator appears to be a simulation of the HP-12C augmented with some HP-11C and the Black Scholes functions.

Apparently, the current edition is best version; the earlier version is not worth downloading.  However, the current version only works on iOS 10 or 11.  Therefore, this will not work on earlier iOS devices (like iPad 2 or iPhone 4S).  That is why I deduct two stars.

Landscape mode makes the Janus Calculator resemble the HP-12C.  Minor glitch, both iPhone SE and iPad Pro:  "Flip" and "i" are not available in landscape mode.  ("Flip" is how to switch between RPN and standard mode; "i" is access to help and other features). No stars deducted for this.

### 5/5 — Amazing

*2011-10-19*

So cool... My best friends daddy made this..... Hehe

### 5/5 — Non math geek

*2010-11-19*

Easy to understand and operate

### 5/5 — Easy interfaces

*2010-09-04*

I'm old enough to remember the early handheld calculators, and what a difference it made to have a calculator with a full instruction set and a sensible interface.  This app does it well, twice, plus offering a few useful constants.  Bravo!

### 5/5 — This is great! Just like my old HP.

*2010-05-28*

Love this.  Works on my ipad.  Well done.

## Frequently asked questions about Janus Calculator

### What makes Janus Calculator unique?

Janus Calculator features a distinctive two-sided interface, allowing users to simultaneously use Standard Notation on one side and Reverse Polish Notation (RPN) on the other. This dual approach caters to different user preferences and calculation styles.

### What types of calculations can Janus Calculator perform?

It supports a wide range of calculations, including programmable functions, various finance and scientific operations, and the values of 45 physical constants. It also includes a specialized Black-Scholes option calculator.

### Is Janus Calculator suitable for financial analysis?

Yes, Janus Calculator includes specific finance functions and a Black-Scholes option calculator, which is a key tool for options pricing and analysis. It also supports implied value calculations for option inputs.

### Does Janus Calculator have ads?

No, Janus Calculator does not contain advertisements. It is a free application without any ad interruptions.

### What devices is Janus Calculator available on?

Janus Calculator is available for iPhone, iPad, and iPod touch devices. It requires iOS 4.0 or later.

### How often is Janus Calculator updated?

The latest version, 2.2, was released on December 12, 2021. While not updated frequently, it offers a stable set of features.

### What is the user rating for Janus Calculator?

Janus Calculator has a rating of 2.0 stars based on one review. This indicates a mixed or potentially negative user reception based on the limited feedback available.

### Can Janus Calculator be used offline?

Yes, Janus Calculator functions as a standalone application and does not require an internet connection to perform calculations. All its features are available offline.

## Version history (last 5 releases)

### 2.3 — 2026-04-29

Update to IOS26

### 2.2 — 2021-12-12

Updated to IOS15

### 2.1 — 2018-11-10

Bug fix for display in certain orientations

### 2.0 — 2017-07-20

Update to iOS 10.3, including 64-bit to eliminate "this will slow down your iPhone" messages.
Support for display in landscape.
Black-Scholes was working on Reverse Polish calculator but not Standard calculator.  Now it works on both.
Fixed stack operation in RPN mode.  
Other minor bug fixes.
"MEM" function to enable display of calculator's memory (to remind you what you saved in register 6, for example.)
Number display now includes commas.
Three assignable buttons for running programs.
Two new stats buttons - skewness of a distribution, and slope/intercept of a regression line.

### 1.0 — 2010-05-26

No release notes.

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## More apps by Geoffrey Domm

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All apps by Geoffrey Domm: https://appshunter.io/developer/373378724

## Related topics

[geoffrey domm](https://appshunter.io/ios/topics/geoffrey-domm)

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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 2026-06-03.*