# Probability vs Scientific Calculator Plus 991

The clearest difference is price: Scientific Calculator Plus 991 at Free against Probability's $1.99. Scientific Calculator Plus 991 also leads on update cadence (fortnightly vs every 3 months) and ratings volume (13K vs 193). Probability's advantage is in-app purchases (none vs 4) and ads (none vs shown). On review sentiment there is nothing between them.

Scientific Calculator Plus 991 is free to download; Probability costs $1.99 up front. Scientific Calculator Plus 991 sells 4 in-app purchases, starting at $1.99 per month. Probability asks for nothing beyond the download.

Probability holds the better App Store score, 4.9 against 4.7. That said, the two scores are not equally well evidenced: Scientific Calculator Plus 991 has 13K ratings behind it against 193, so its average is the more settled of the two. Written reviews point the same way: 97% of Probability's written reviews are positive against 92% of Scientific Calculator Plus 991's.

Probability ships an update every 3 months, Scientific Calculator Plus 991 fortnightly. The most recent releases landed on November 6, 2026 and November 9, 2026 respectively.

## The numbers

| Metric | Probability | Scientific Calculator Plus 991 |
| --- | --- | --- |
| Price | $1.99 | **Free** |
| Rating | **[4.9 (193 ratings)](https://appshunter.io/ios/app/probability-distributions/id889106396/reviews)** | [4.7 (13K ratings)](https://appshunter.io/ios/app/scientific-calculator-plus-991/id1449106995/reviews) |
| Number of ratings | 193 | **13K** |
| Positive reviews | **97.2% of reviews** | 91.7% of reviews |
| In-app purchases | **No** | Yes |
| Ads | **No** | Yes |
| Update frequency | Every 3 months | **Fortnightly** |
| Monetization | **Free** | Free with in-app purchases |
| Size | 7 MB | 169 MB |
| Requires iOS | 26.0 | **15** |
| Devices | iPhone | **iPhone, iPad, iPod, Mac** |
| Age rating | 17+ | 12+ |
| Developer | [Matthew Bognar](https://appshunter.io/developer/889106399) | [Tran Duy](https://appshunter.io/developer/1449106994) |

## What reviewers say

### Probability

[App page](https://appshunter.io/ios/app/probability-distributions/id889106396)

Calculate probabilities, find percentiles, and visualize probability density or mass functions for a wide range of continuous and discrete statistical distributions. Explore common distributions like normal, binomial, Poisson, and many more.

**Highlights:** Compute probabilities, Determine percentiles, Plot probability density function, Plot probability mass function, Supports 10+ continuous distributions, Supports 5+ discrete distributions

**Features:** Vision Pro support

**In-app purchases:** none

**What reviewers like**

- 👍 Easy to use interface
- 📊 Great for probability distributions
- 💡 Useful for checking work and homework
- 💰 Free advanced functions
- 📈 Visualizes data and distributions

**What reviewers complain about**

- 🚫 Not allowed on some exams
- 🤔 Some users want more features

**Requested features**

- Exam mode similar to Geogebra
- Poisson distribution
- Allow setting plot boundaries (e.g., for Beta distribution)
- Make formulae available in offline mode
- Clearly introduce parameters


### Scientific Calculator Plus 991

[App page](https://appshunter.io/ios/app/scientific-calculator-plus-991/id1449106995)

This app is a powerful scientific calculator with graphing capabilities, a formula library, and a unit converter. It offers natural display input, advanced math functions for algebra, calculus, and statistics, and supports various number bases and formats.

**Highlights:** Natural display input, Graphing module, Formula library, Unit and currency converter, Algebra and calculus tools, Matrix and vector operations, Statistical calculations

**Features:** Family Sharing, Vision Pro support

**In-app purchases (4)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Calculator month subscription | $1.99 | per month |
| Calculator yearly subscription | $3.99 | per year |
| Calculator Premium | $5.99 | one-time |
| Calculator Pro | $5.99 | one-time |

**What reviewers like**

- 👍 Intuitive and easy to use
- 🚀 Powerful and feature-rich
- 💡 Customizable interface and settings
- 🔍 Extensive library of formulas and equations
- ⚙️ Handles complex math and scientific functions well

**What reviewers complain about**

- 🐛 Occasional bugs and input issues
- 🔀 Confusing layout and button placement
- 💰 Some advanced features locked behind paywall

**Reported bugs**

- Keyboard input stops working after switching screens
- Incorrect calculation results for certain operations
- App crashes on some devices after recent update

**Requested features**

- Add option to change display font and color
- Improve cursor control and editing capabilities
- Implement auto-simplification for complex expressions
- Add more handwriting font options
- Expand graphing and equation solving features


## Frequently asked questions

### Is Probability free?

Probability costs $1.99, with no in-app purchases.

### Is Scientific Calculator Plus 991 free?

Scientific Calculator Plus 991 is free to download, with in-app purchases available.

### Which has better reviews, Probability or Scientific Calculator Plus 991?

Probability is rated higher. Probability averages 4.9 out of 5 from 193 ratings, while Scientific Calculator Plus 991 averages 4.7 from 13K ratings.

### Do Probability or Scientific Calculator Plus 991 have ads?

Scientific Calculator Plus 991 shows ads; Probability does not.

### Which is updated more often, Probability or Scientific Calculator Plus 991?

Probability ships an update every 3 months, and Scientific Calculator Plus 991 fortnightly. Most recently, Probability was updated on November 6, 2026 and Scientific Calculator Plus 991 on November 9, 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.*