Dear [Friend's Name],

I hope this letter finds you well. I am writing to invite you to my birthday party! It's going to be a fun-filled evening and I would love your company to make it even more special. The party is scheduled for [Date] at [Time]. We will be celebrating at [Location]. Your presence means a lot to me and I really hope you can make it.

Looking forward to seeing you there!

Best Regards,
[Your Name]