Future perfect and future continuous
The future perfect ("will have done") describes an action that will be completed before a specific point in the future, while the future continuous ("will be doing") describes an action that will be in progress at a specific future moment.
Future Continuous: action in progress
We use the future continuous (will/won't + be + verb-ing) to talk about an activity that will be happening at a particular time in the future. It emphasises that the action will be ongoing, not finished, around that moment. We often use it with time expressions such as 'at 8 o'clock', 'this time tomorrow', or 'all day'.
- •This time tomorrow I'll be flying to Madrid.
- •Don't call at 7 p.m. — we'll be having dinner.
- •She won't be working next Monday because it's a holiday.
Future Perfect: completed before a deadline
We use the future perfect (will/won't + have + past participle) to say that an action will be finished before a certain time or before another future event. It looks back from a point in the future to an action already completed by then. It usually appears with 'by', 'by the time', or 'before'.
- •By 2030 the company will have opened ten new offices.
- •Call me at six; I'll have finished the report by then.
- •By the time you arrive, they won't have left yet.
Comparing the two tenses
The key difference is whether the action is still in progress or already complete at the future moment you mention. Use the future continuous for something happening at that time, and the future perfect for something already done before that time. Choosing the right one depends on the time marker: 'at/this time' usually signals continuous, while 'by/before' usually signals perfect.
- •At 9 a.m. I'll be writing emails. (in progress)
- •By 9 a.m. I'll have written ten emails. (completed)
- •This time next week she'll be lying on a beach, and by August she'll have visited five countries.
Common errors and useful phrases
Remember that 'be' and 'have' do not change form: it is always 'will be' and 'will have', never 'will am' or 'will has'. After 'by the time', use the present simple, not a future form, even though the meaning is future. Questions invert the subject and 'will': 'Will you be working?' or 'Will they have finished?'.
- •By the time the train leaves, we'll have boarded. (NOT 'will leave')
- •Will you be using the car tomorrow afternoon?
- •How long will they have been here by Friday?