there's no telling
It's impossible to determine, as in There's no telling how many children will come down with measles, or There's no telling what will happen in the next episode of that soap opera. This idiom uses telling in the sense of “reckoning,” a usage dating from the late 1300s.
- there's no accounting for taste,
- there's no accounting for tastes,
- there's no fool like an old fool,
- there's no place like home,
- there's no smoke without fire,
- there's no time like the present,