This is what I do but I don't try to make it complicated with too many numbers. "2 weeks but there's a 10% chance something bad happens and it takes longer".

I have no problem if they just hear the "2 weeks" part. If they come complaining in 3 weeks I just say "we hit that 10%".

The other important thing is to update estimates. Update people as soon as you realise you hit the 10%. Or in a better case, in a week I might be able to say it's now "1% chance of taking more than a week".