Online poker equity calculators not consitent

Question

I'm developing a poker software for some time already, and decided to compare the results of my game with several popular online poker equity calculators.

I'm surprised that out of 4 different calculators only one matches the results that I'm generating.

Example cards / my results:

Player 1: 8cKs / 98.58%

Player 2: Kh4d / 1.41%

Board: 5c8s9h

This are the sites I visited for comparison:

Site 1: 97% vs 0,3 %

Site 2: 63,5% vs 0,3%

Site 3: Same as mine

Site 4: 97.47% 0,30%

Why is this so? How can these results be different? the math is very simple and math can't produce different results if correct calculation is done.

Can you explain this, and how do we get 100% correct results? because those online calculators obviously can't be trusted, they don't even match between them self.

Answer 1

Your result adds up 1 (98.58% + 1.41%) and Site 1 and 4 do not, which means you do not calculate the tie case separately, while they do. This is definitely a difference in methods.

Without computation on this particular hand and by looking at the numbers only: With site 4: 98.58-97.47 = 1.41 - 0.3 = 1.11%. So the probability of tie should be 2.22% which you do not separately calculate.

Site 1 rounded up I think and Site 2 looks wrong.

Answer 2

I can not say for sure why these sites produce different results. It is very possible that it is because the developers of these sites may have taken shortcuts when calculating the equity of each hand.

A good calculator that is 100% correct that I like to use is pokerstove. It is 100% correct because it uses a large number of simulations rather than math to produce a result.