If someone has good news, they might say:
- I passed my exams
- The doctor said that I'm okay
- I'm engaged!
- I'm pregnant!
- We're spending our summer in America.
You might reply:
- I'm so glad!
- Oh, how lovely!
- Wow, that's amazing!
- That's fantastic!
- That's great!
You could also say:
- I'm so pleased for you!
- What wonderful news!
- I'm so happy for you!
You could use an idiom and say:
- I'm over the moon for you!
- I'm pleased as punch for you!
If you want to continue the conversation, you could say:
- You must be really happy.
- You must be so proud of yourself
- Is your boyfriend pleased about the news?
- Are you excited?
- Are you looking forward to it?