The actor says he's even harder on himself than the harshest online troll.
Marvel's Doctor Strange is looking at his work in a new light thanks to his production company, SunnyMarch, which is behind The Child In Time.
The 41-year-old not only plays the lead role in the first ever TV adaptation of an Ian McEwan novel, but is the BBC One drama's executive producer as well.
Cumberbatch stars as Stephen Lewis, a children's author whose world falls apart when his four-year-old daughter goes missing in a supermarket.
He says getting to adapt the Whitbread Prize-winning book - which tells of how Stephen's life and that of his wife Julie diverge after the loss - was a "huge boon".
Yet the actor admits it's "different when you've got a producer's hat on. If you're front and centre, that's really hard.
"I'm excited about the moment when I'm not in something and I can look at it with more more distance, but it's very peculiar.
"It's always horrible - the way you look, the way you do things. It's just horrible.
"Trust me, the internet's full of hate but it's nothing compared to the self-critic in your head for brutality. I've said it all before they have."
Cumberbatch says he had a "great experience" making the drama, a joint production with Pinewood Television.
"I didn't choose it. It chose us, really," he goes on. "It just worked - the timing was right, it was a brilliant script first of all and it's an extraordinary novel."
The actor, who has two young sons with his wife Sophie, says the situation of losing a child while looking away in a familiar environment is "horrifically relatable".
"It's a part that is a million miles away from all the stuff I've done - especially the more famous one on telly - and that's an appeal for me.
"I'll always be shaking things up a little bit as far as expectations are concerned - not doing the usual or the unusually usual - and the extreme nature of the situation [in The Child In Time] is very unusual.
"I don't think you have to be a parent to understand," he continues. "There are fantastic actors out there I've seen give extraordinary performances of parents in crisis, or just parents in fictional roles.
"It wasn't like 'oh great, I can get my teeth into something whereby I'll be emotionally raw because I'm a new dad for the second time.' It just happened that way."
Speaking of that more famous telly role, would he like to do more Sherlock? All he'll say, with an enigmatic smile, is "maybe".
At the time we speak, it's just been announced that Jodie Whittaker is taking on the lead role in Doctor Who - the first woman to do so.
Cumberbatch is thrilled about this and says he can't wait to see her performance. "It's an alien - why can't it be a woman?" he says.
"Why can't it be any gender? I think she's an extraordinary actress and we're lucky culturally to have got her to agree to do it. Just go for it - let's see what happens."
Would he be just as up for seeing a female Sherlock? "Why not? I don't care," he says, adding tongue-in-cheek: "Sherlockina - it's coming to you soon."
SunnyMarch, he points out, has a lot of plans for improving diversity and "giving a bolder place for women both behind and in front of the camera." Watch this space.
The Child In Time will be shown on BBC One on 24 September at 21:00 BST.