# The Essential Magical Probability Guide!



## ChaosRedCorsairLord

Ok, admittedly it's not absolutely essential, I just wanted to feel special...

During a recent 8th ed game, during my opponent's magic phase, it became apparent to me that some people have no idea when it comes to "dice probability". My opponent started to get confused as to how many PD & DD he should be using. Now I realize that there is no absolute "correct amount" of PD you should be using to cast a spell, it's a bit of a personal choice depending on how many PD you have to spare and how willing you are to risk the dreaded Miscasts of 8th ed.

I myself am pretty good when it comes to probability, statistics and mathematics in general. So to help out those of you who aren't Rain Man I've made a simple table to give a percentage representation of rolling chances with different amounts of PD/DD and the miscast chances. There are probably better guides out there, this is just a simple single page table. Also, I did these calculations mostly by hand/mental maths/patterns, so there may be some mistakes in there, particularly in the miscast chances (which I scribbled out in about 10 mins) and the 6D6 probabilities, which I had to rely on a mathematical pattern for. Hope it helps.

*General Info:*
Average Power Dice generation (Addition of 2D6) = 7 PD (+ n/6)
Average Dispel Dice generation (2D6, pick highest) = 161/36 = 4.47 DD (+ n/6)
(n = number of channelling wizards)
CVs: Cast Values.
MCs: Miscast Percentages.

[I've attached an MS doc version]

Here's the best I could do using forum text:

*CVs _1D6 _2D6 __3D6 __4D6 _5D6 __6D6*
03+	66.7%	97.2%	100% 00.0%	00.0%	00.0%
04+	50.0%	91.7%	99.5%	100% 00.0%	00.0%
05+	33.3%	83.3%	98.1%	99.9%	100% 00.0%
06+	16.7%	72.2%	95.4%	99.6%	~100%	100%
07+	00.0%	58.3%	90.7%	98.8%	99.9%	~100%
08+	00.0%	41.7%	83.8%	97.3%	99.7%	~100%
09+	00.0%	27.8%	74.1%	94.6%	99.3%	99.9%
10+	00.0%	16.7%	62.5%	90.3%	98.4%	99.8%
11+	00.0%	08.3%	50.0%	84.1%	96.8%	99.5%
12+	00.0%	02.8%	37.5%	76.1%	94.1%	99.0%
13+	00.0%	00.0%	25.9%	66.4%	90.2%	98.0%
14+	00.0%	00.0%	16.2%	55.6%	84.8%	96.4%
15+	00.0%	00.0%	09.3%	44.4%	77.9%	93.9%
16+	00.0%	00.0%	04.6%	33.6%	69.5%	90.4%
17+	00.0%	00.0%	01.9%	23.9%	60.0%	85.5%
18+	00.0%	00.0%	00.5%	15.9%	50.0%	79.4%
19+	00.0%	00.0%	00.0%	09.7%	40.0%	72.1%
20+	00.0%	00.0%	00.0%	05.4%	30.5%	63.7%
21+	00.0%	00.0%	00.0%	02.7%	22.1%	54.6%
22+	00.0%	00.0%	00.0%	01.2%	15.2%	45.4%
23+	00.0%	00.0%	00.0%	00.4%	09.8%	36.3%
24+	00.0%	00.0%	00.0%	00.1%	05.9%	27.9%
25+	00.0%	00.0%	00.0%	00.0%	03.2%	20.6%
26+	00.0%	00.0%	00.0%	00.0%	01.6%	14.5%
27+	00.0%	00.0%	00.0%	00.0%	00.7%	09.6%
28+	00.0%	00.0%	00.0%	00.0%	00.3%	06.1%
29+	00.0%	00.0%	00.0%	00.0%	00.1%	03.6%
30+	00.0%	00.0%	00.0%	00.0%	~0.0%	02.0%
31+	00.0%	00.0%	00.0%	00.0%	00.0%	01.0%
32+	00.0%	00.0%	00.0%	00.0%	00.0%	00.5%
33+	00.0%	00.0%	00.0%	00.0%	00.0%	00.2%
34+	00.0%	00.0%	00.0%	00.0%	00.0%	00.1%
35+	00.0%	00.0%	00.0%	00.0%	00.0%	~0.0%
36+	00.0%	00.0%	00.0%	00.0%	00.0%	~0.0%
MCs	00.0%	02.8%	07.4%	13.2%	19.6%	26.3%

*How The Table Works:*
Find the spell you want to cast’s cast value, and then minus any caster bonuses you have from the cast value (Eg: Lvl 3 Vampire lord with skull staff attempting to cast Purple Sun; 15 – 4 = 11). Then basically look at that value on the table to compare the probability of the spell being successfully cast on different amounts of PD.

Dispelling is similar. Get your opponent’s modified roll value, minus any Dispell bonuses you have then consult the table.

Finally: If you see any mistakes or errors in the calculations or rules I've misread feel free to point them out, it's still a work in progress.

PS: Sorry for all the red text mods!

CRCL out!


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## ChaosRedCorsairLord

*Just to expand on the example and how to use the table:*

*Vampire Lord* (the army general)
-Lvl 2 (+2 to cast/dispell).
-Skull Staff (+1 to cast/dispell).

So, my Vampire Lord has, in total, a +3 bonus to cast/dispell. I want to cast the Death spell; Purple Sun, which has a cast value of 15+. So, to use the table all I need to do is get the spell's cast value (15) and minus my caster's bonus to cast (3). This will give me the actual amount I need to roll for the spell to b successfully cast, which in this case is 12+ (15-3=12). 

So, I go to the row on the table labelled 12+. I also want to take the miscast chance into account (located at the bottom of the table). The two rows read as follows:
*CVs _1D6 _2D6 __3D6 __4D6 _5D6 __6D6*
12+	00.0%	02.8%	37.5%	76.1%	94.1%	99.0%
MCs	00.0%	02.8%	07.4%	13.2%	19.6%	26.3%

To reliably cast this spell, without wasting PD I'd be looking to use either 4 or 5 D6:
*4D6* - 76.1% chance of success, with a 13.2% chance of miscast.
*5D6* - 94.1% chance of success, with a 19.6% chance of miscast.
Because my Vampire Lord is my general and I really want to minimize his exposure to the dreaded miscast table, I would choose to use 4D6 as opposed to 5D6.

Obviously you could use 3D6 or even 2D6 if you are short on dice, the spell isn't particularly necessary or you do not want to risk the chance of a miscast.

User Beware!: While the table does show miscast/IF chances, it does not take into account that miscasts are auto-passes. It also does not integrate the miscast chances into the main table, so the values are not absolutely accurate, especially in the 6D6 column. So use some common sense too!


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## OldHat

...who put "no"!?! This is AWESOME!


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## LukeValantine

So if I take a level 1 VC with lore ob beasts I can half more then half my chances of miscast, and still have a 60% chance of casting transformation if I take a power stone. Hmm...


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## Whizzwang

Wow awesome, someone has copied my probability table from last year. Kudos, must give you rep for that.

EDIT: link added http://www.heresy-online.net/forums/showthread.php?t=52050


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## ChaosRedCorsairLord

Whizzwang said:


> Wow awesome, someone has copied my probability table from last year. Kudos, must give you rep for that.


Well that's just annoying, I thought I'd done something original for once. Your table is so much prettier than mine too. Just curious, did you use tables & calculations or the table pattern to work out the probabilities? 
Also I didn't 'copy' your table, I did all my own calculations and if I had realized someone else had already made such a table I wouldn't have bothered going to all the effort. Having said that, some of the similarities between not just the table, but things we've both posted in the threads is downright scary.


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## LukeValantine

Considering that probability tables would look identical it is entirely possible that both of you created these charts separately, and at different times without prior knowledge of each others works.


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## ChaosRedCorsairLord

Ah well. Now I can double check my maths. Already spotted one mistake. Not sure how I got 12281/46656 = 0.402.


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## Durzod

New Math??


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## Zaden

Thanks for this CRCL. I can't view Whizz' from work and your attitude is better so have some rep.


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## Alvraad

These tables are old news. Even I've done one on another forum once. Though mine had to do with a special item along with the probability so it was slightly more original until someone corrected a mistake I had and ended up lapping up half the praise. However, it is still really useful for everyone who plays table top to mess around with dice probability.


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