We generally use by/in with the future continuous and by/in with the future perfect.

By the time you arrive I _______ something spectacular and dinner will be on the table waiting for you. [ a. will have cooked ] [ b. will be cooking ]

I'm taking the day off on Friday – I ______ be working.

Our table at the restaurant is at 1 p.m. Do you think we'll have ________ lunch by 3 p.m.?

We form the future perfect with - will + have + present/past participle.

There won't be anyone in the office. Everyone _____________ (go) home.

In less than 2 years, my grandparents _______ for 50 years. We are going to celebrate it. [ will have been married ] [ will be getting married ]

When I travel to England next year I ________ English for over four years, so I think I'll be ready. [ will be studying ] [ will have studied ]

Please, come at 8. By that time, I ______ my homework and we can go out. [ 'll be finishing ] [ 'll have finished ]

We are visiting a new city every week. By the end of the summer, we _______ all the most important cities in Europe. [ will be visiting ] [ will have visited ]

When we arrive in Los Angeles we'll need to rest, because we _______ about 800 miles. [ a. will be driving ] [ b. will have driven ]

In their retirement, they'll _______ living in a small house in the mountains.