On To vs. Onto

On To  vs.  Onto


onto

Rule 1
In general, use onto as one word to mean on top of, to a position on, upon.
If you can use up before on, use onto.


He climbed (up) onto the roof. 
Let’s step onto the dance floor.

Rule 2
Use onto when you mean fully aware of; informed about.

We canceled Julia's surprise party when we realized she was onto our plan.


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on to
She held on to her child in the crowd. (She did not hold up her child.)
I’m going to log on to the computer.