I'm going to
I'm gonna
/aɪm ˈɡʌnə/Reduction
In real speech
What happens to the sounds
“going to” squeezes into one unstressed syllable: -ing disappears and to becomes /ə/ → “GUN-na”.
When to use it
Only for the future (I'm gonna call her). When it means moving somewhere (I'm going to the shop), people don't say gonna. In writing — only in texts.
Casual → formal
Slang
I'm gonna
Neutral
I'm going to
Formal
I intend to
Sound notes
Reduction: unstressed words get squeezed, and their vowels turn into the neutral sound /ə/.