On to vs. Onto

 

Rule 1: Use onto as one word if you can add up before on.
Example: He climbed (up) onto the roof.
Example: She held on to her child in the crowd. (She did not hold up her child.)
Rule 2: Use onto when you mean fully aware of; informed about.
Example: We canceled Julia’s surprise party when we realized she was onto our plan.
Click here to learn hundreds of distinctions between common words.
Posted on Wednesday, January 6th, 2010 at 8:53 am

http://data.grammarbook.com/blog/definitions/on-to-vs-onto/