These two words mean exactly the same. They can be used both as prepositions and conjunctions. Note that until is more formal than till.
- I will wait until/till I hear from you.
- Wait until/till tomorrow.
- Wait until/till he returns.
Until/till and to
To can sometimes be used as a preposition of time with the same meaning as until/till. This happens after from …
- I usually work from ten to six. (OR I usually work from ten until/till six.)
Cases where until/till is not used
Until/till is used only to talk about time. To talk about distance, we use to, as far as or up to; up to is also used to talk about quantity.
- We walked as far as/up to the edge of the forest. (NOT …until/till the edge of the forest.)
- You can earn up to $100 a week.
It is sometimes possible to use until/till before a place name in the sense of ‘until we get to …’.
- Go straight on until/till you come to the post office and then turn left.
Tenses after until
After until, we use present tenses to refer to the future.
- I will wait until she returns. (NOT … until she will return.)