The spreadsheet is pretty basic. You enter the values for the variables in the blue cells, like STAB, boosts, etc, and the offensive and defensive stats for each mon and it gives you a min and max roll. I just can't get my min/max to match showdown's results.

Would anyone be able to check out my calculator and help me find out what is making my results slightly off? I feel like it has to come down to rounding somewhere and I've triple checked everything twice. The formula I'm using to get a damage percentage is shown below. This is getting me the results I show in the example below.

=(FLOOR.MATH(FLOOR.MATH(FLOOR.MATH(2*100/5+2)*BasePower*Attack/Defense)/50)+2)*Modifier/HP

Where the showdown calc gives this:

252+ SpA Life Orb Triage Charizard-Mega-Y Oblivion Wing vs. 252 HP / 252 SpD Kartana: 320-376 (99.3 - 116.7%) -- 87.5% chance to OHKO

My calculator gives the min roll as 99.0% and max roll as 116.5%.