“No, I'm good. I had a late lunch.”
You're visiting a friend's house in the evening. He's going to order dinner from a restaurant. He asks if you want anything to eat, but you're full already.
No, I'm good. I had a late lunch.
"I'm good" is a casual expression that means "No thanks."
You can respond "I'm good" when someone offers you something (like food) but you don't need it:
A: Here, have a piece of cake.
B: No, I'm good.
Use it with friends, coworkers, and family members.
A "late lunch" means that you ate lunch later than usual.
People use this phrase to explain why they're not hungry at dinner time:
I'm not really hungry. I had a late lunch.