When to throw the engagement party ?

Typically engagement parties are thrown by someone else, like a friend or family member, within 2-3 months of the proposal.

I would say no later than one month before the wedding. Ine friend did it early and one did it a few months before.

I would say soonish?? Otherwise you’ll run into Showers. We also got engaged in Sept and had an informal Engagement Party (at a bar with local friends and family) within 2 weeks. Good luck!

As soon as possible after the engagement, if that is less than a year away. Often parents or other older family give them. But the longer the B and G have been living on their own, the more likely it is they will give one on their own, especially if they live far from family, and most attendees will be their own friends and work people, with few family. I don't know anyone mid thirties or older , on their own since high school or college, who had one girl en by family. Many had a family only dinner, and the general engagement party was given by the couple themselves. When people have a long engagement, planned from the start to be 2,3,4 years, like for school, military service, they often announce the engagement immediately. But have an engagement party at one year out, and announce their wedding party and plans only after that. The party signals the active last year of planning, whatever ER has happened before being behind the scenes stuff. That is really the only time the party is not given immediately after the engagement itself.
Sometimes by 3 years later, they live in a different place, and have totally different friends, than years back when they actually got engaged, so doing it at the last year point makes sense.