Here is the heart of it:
People confuse the two - it's and its - because normally an apostrophe indicates possession, as in Dave's or Jan's.
When used with the word 'it,' the apostrophe indicates a contraction, like in can't or won't.
Here is the test:
- If the contraction of 'it is' can be replaced by 'it has' or 'it is' it's 'it's.'
- Otherwise it's 'its.'
- It has been a long time = It's been a long time.
- It is my finger = It's my finger.
- It is time to glue your mouth shut = It's time to glue your mouth shut.
- That slave needs to lose some of its attitude.
- The wagon has lost its wheels.
- That car would look better with its doors attached.