Readless I would be folding here. We do block the some KT9x combos and yes they can have busted draws, but until I see them do something like this with a busted draw I would just be expecting a KT9x hand and fold. I think likely by checking back you avoided what would have been a checkraise on the flop.

http://imgur.com/a/JaJlI

So if we break it down, and think he is only donking for value with KT on the river,

We need to be correct 33% of the time and hes gonna show up with KT 23% of the time and hands that might bluff like missed spades with a K or a T , KK , TT , or just a K or just a T

If my calculations are correct, 50% of the time hes gonna get to the river with a blocker that might want to bluff the river, how often he uses those blockers, i guess thats player dependant,

And can someone maybe help me to calculate how much of his bluffs he needs to donk here to make it profitable?

Is it as simple as he needs to use 1/5 of those to bluff with to add up for the required pot odds needed ?

You are getting 2:1 which is 33% on a call if he pots. You need 33% to break even. Therefore if "hes gonna show up with KT 23% of the time" he needs to have bluffs for the remainder. This depends on what you mean by 23% of the time. Are you meaning that 77% of the time he has bluffs when he bets? Or that 23% of the 33% we need is KT?

If 77% of the time he has bluffs, we should call 100% of the time.

If 23% of the 33% we need to breakeven he has KT he needs to have bluffs for the remaining 10% which equates to him needing to have bluffs roughly 1/3rd of the time, or in a 2:1 ratio of KT to bluffs.

You may also be saying that 23% of his range at the river is KTxx, therefore how much of his 77% bluffs does he need to be betting to make this a profitable call. If it is 10% as above (23% to 33%+) then he would need to be bluffing with more than 13% of his 77% to make the 10% or more bluffs, or roughly 2 out of every 15 busted hands he needs to be bluffing with. (10/77*100 to make it a % = 13% and 100/13 = 7.7 so 6.7:1 for his bluffs or 13:2 with rounding which is the same as 2 out of 15; 1:3 is the same as 1/4, 2:3 is 2/5 in terms of writing ratios as fractions)

I am tired this may not make sense or address your question.

Its this simple. If he has 23% for value we need half of those combos for the odds to be 2:1. So a total % of 11.5% and we have the odds to call.

So yeah 11.5% out of the 50% ~ 1/5.

Very good post @ProJondi !

thx guys, i called and he had KKT