Here's a link to the Google Sheets version, which you can make a copy of and then select whatever settings you want for your desired riven. Unfortunately if you try to download it as an Excel file, the checkboxes won't copy over properly, so you'll want to stick with the Google Sheets version. I actually had to remake the checkboxes from scratch after importing my original Excel file into Sheets since none of the checkboxes transferred over, so I guess there's some kind of compatibility issue with checkboxes.
Hopefully the calculator should be pretty selfexplanatory, but I'll briefly go over it:

The first sheet (Input+Info) is where you input all your settings (highlighted in blue) for your desired riven, and also where the probability, kuva cost, etc are displayed. The calculator will calculate the total number of possible rivens that contain only the stats you've selected as desirable, then use that to tell you the probability of getting a good roll. It will also tell you the number of rerolls you'd have to perform in order to have x% cumulative chance to get a good roll, how much kuva that would cost, and even how long it would take to farm that much kuva.

The second sheet (Possible Stats) is just a nice reference for what stats are possible for rivens of each weapon type; boxes with an X show that the stat is possible on the riven, while blank or greyed out boxes show that the stat isn't possible. For example, cell C9 has an X, meaning Rifles and Pistols can have Critical Damage as a negative stat.

The third and final sheet (Calculations) is, well, all the equations I used to get the data that's displayed on the first sheet. I want to give a big shoutout to Sunofthebeach25 on the Warframe Wiki for his post about the probability of different riven rolls. I used a slightly altered version of his method to calculate the number of possible rivens with good rolls, and without his post it would've taken me a lot longer to figure out how to calculate all this.
Limitations of the calculator:
 The calculator currently cannot tell you the probability of getting a riven that doesn't have exclusively desired stats. For example, it can't tell you the probability of getting a riven that has 3 positive stats, with only 2 of those stats being desirable. So if you wanted a riven with 3 stats, where two of them are damage and multishot but the 3rd stat could be anything, the calculator couldn't tell you the odds of that. Basically the calculator only looks at the possible rolls that strictly contain stats that you've specified as desirable.
Assumptions of the calculator:

All possible stats have an equal probability of being rolled

Each of the 4 riven "sizes" has an equal chance of being rolled. In other words, any given roll has a 25% chance to be 2+/0, 2+/1, 3+/0, or 3+/1

When the stats on a new roll are being generated, positive stats are generated first, and then the negative stat (if present) is generated from the remaining list of possible, nonconflicting negative stats.
Hope you guys find this as interesting / useful as I do! And let me know if there's anything I can clarify, or something I messed up!
– Source
Similar Guides
 365 Days of Sorties: Round III (2020)
 Icon Swaps 3 – Icon Pick Dynamic Probabilities SPREADSHEET
 Improvements to card RNG
More about Warframe
Post: "I made a riven calculator that tells you the probability (and kuva cost) of getting your desired roll. Fully customizable and easy to use!" specifically for the game Warframe. Other useful information about this game:Top 20 NEW Medieval Games of 2021
Swords, dragons, knights, castles  if you love any of this stuff, you might like these games throughout 2021.
10 NEW Shooter Games of 2021 With Over The Top Action
We've been keeping our eye on these crazy action oriented first and third person shooter games releasing this year. What's on your personal list? Let us know!
Top 10 NEW Survival Games of 2021
Survival video games are still going strong in 2021. Here's everything to look forward to on PC, PS5, Xbox Series X, Nintendo Switch, and beyond.