Use it's when the subject is it and the main verb is is.
The apostrophe (') between it and s is required.
Use its when you are referring to something already mentioned and it is not the subject of the sentence.
There is no apostrophe (') between it and s.
The check your writing for its/it's, use the following steps:
Circle the subjects and underline the main verbs in all of your sentences.
In each sentence, find each it. When it is the subject and is is the verb, you can use it's.
For each it that is not a subject and that refers to something previously mentioned, use its.
Read your writing out loud. Say "it is" whenever you see it's or its.
Write or paste your writing into Microsoft Word. The grammar checker underlines some its/it's errors.
The Spelling and Grammar tool sometimes show you its/it's errors and suggests corrections.
Word does not find all errors, so it is better to use steps 1-4 to proofread your writing.
Circle all subjects and underline all main verbs in your sentences
If your subject is it and your main verb is is, us it's.
If it refers to something else previously mentioned, use its.
Read your sentence out loud. Say "it is" for every it's or its. Does it sound right?
Use Microsoft Word's grammer checker to check it's/its.