I voted 60-70 %, but after doing some calculations, it is probably a bit lower.
First we have to estimate the chance of him not being affected by crashes or illnesses to the extend that will hinder him from performing at his peak or close.
I looked at last years Tour, where 25 dnf'd out of 176 riders, this doesn't directly translate to Pogacar's situation, as some of these riders were outside time limit, pulled out because of poor shape/fatique while some might have completed despite having crashed so hard they couldn't compete at their best level. Pogacar is also better at handling and positioning than most, so lets say for every stage he competes, he has 169/170 chance of not being severely affected by crashes or illness.
That gives him (169/170)^21 = 88.35 % chance of getting through the giro without getting GC ruined by a crash or illness. Then there is the chance that he might be beaten by a stronger rider, I consider that unlikely, but lets give Thomas and anyone else 2 % chance combined to win over Pogacar on strength. Then he has 0.8835*0.98 = 86.58 % chance of winning the Giro. He has no race days between Giro and Tour, but he could crash badly during training, let's say there is a 1 % chance that happens, now he is down to 85.71 %. He likewise has an 88.35 % chance of not getting his Tour ruined by illness or crashes, that puts him at 0.8571*0.8835 = 75.73 %.
Then finally there is the big question, will he be strongest at the Tour with the Giro in the legs, and Vingegaard potentially recovered (how much?), and how good are Roglic, Evenepoel, Bernal, Hindley? I give him 65 % chance of being the strongest, so:
0.7573*0.65 = 49.22 %.
So I give him just short of 50 % chance of doing the double.
First we have to estimate the chance of him not being affected by crashes or illnesses to the extend that will hinder him from performing at his peak or close.
I looked at last years Tour, where 25 dnf'd out of 176 riders, this doesn't directly translate to Pogacar's situation, as some of these riders were outside time limit, pulled out because of poor shape/fatique while some might have completed despite having crashed so hard they couldn't compete at their best level. Pogacar is also better at handling and positioning than most, so lets say for every stage he competes, he has 169/170 chance of not being severely affected by crashes or illness.
That gives him (169/170)^21 = 88.35 % chance of getting through the giro without getting GC ruined by a crash or illness. Then there is the chance that he might be beaten by a stronger rider, I consider that unlikely, but lets give Thomas and anyone else 2 % chance combined to win over Pogacar on strength. Then he has 0.8835*0.98 = 86.58 % chance of winning the Giro. He has no race days between Giro and Tour, but he could crash badly during training, let's say there is a 1 % chance that happens, now he is down to 85.71 %. He likewise has an 88.35 % chance of not getting his Tour ruined by illness or crashes, that puts him at 0.8571*0.8835 = 75.73 %.
Then finally there is the big question, will he be strongest at the Tour with the Giro in the legs, and Vingegaard potentially recovered (how much?), and how good are Roglic, Evenepoel, Bernal, Hindley? I give him 65 % chance of being the strongest, so:
0.7573*0.65 = 49.22 %.
So I give him just short of 50 % chance of doing the double.