Into and in to sound the same, but they are not always interchangeable.
Use into as one word when it shows movement from outside to inside, or a change in direction toward something. For example: She walked into the room. You can also write, The car turned into the driveway.
Use in to as two words when in is part of the verb or phrase before to. In that case, to usually connects to what comes next. For example: Please log in to your account. Here, log in is the phrasal verb. Another example is She came in to help. In that sentence, came in is the phrase, and to help explains why.
- into: movement or direction, go into the house
- in to: in belongs with the verb, check in to the hotel
A useful test is this: if you can replace it with inside, into is often right. If the verb naturally ends with in, such as log in or check in, then in to may be correct.
