1. First, choose your viewpoint
Imagine a future meeting and look back from it at the work done before then. The question might be “What will already be done?” or “What process will have continued, and for how long, by that time?” Both viewpoints can concern the same project.
By Friday sets the viewpoint’s boundary, but it does not by itself choose Simple or Continuous. The future point can also be named with on Monday, in June, when you arrive, or established in a previous utterance. The preposition depends on the meaning of the time phrase.
By Friday, we will have prepared the exhibition guide.
By Friday, we will already have prepared the exhibition guide.
The focus is on the guide being ready by the future boundary.
By Friday, we will have been preparing the exhibition for a month.
By Friday, we will have been preparing the exhibition for a month.
We are summing up the preparation time; this sentence does not confirm that the entire exhibition will be ready.
2. Result and activity are different messages
Future Perfect Simple with an action that has a clear result presents that result as achieved by a future point: have written the summary, have repaired the lift. Continuous describes the activity; it does not confirm that its result is ready.
Do not mechanically replace one construction with the other. If all that is known is that negotiations have continued for a long time, you cannot rephrase this as a signed contract: you would be adding a new fact.
By noon, the team will have repaired the lift.
By noon, the team will already have repaired the lift.
The repair is presented as a completed result.
By noon, the team will have been repairing the lift for four hours.
By noon, the team will have been repairing the lift for four hours.
Four hours of work does not tell us whether the lift will already be working.
3. Simple can also express duration
With work or live, both forms can be natural. Simple allows you to sum up a period of experience or residence; Continuous emphasizes the course of the activity more clearly. The words for six years do not make Continuous the only correct answer.
Simple does not necessarily mean that something will stop. If it is said that by June a person will have lived here for five years, this does not imply that they will move in June. For states, Simple is often used: will have known, will have owned, will have been a member.
In June, I will have lived here for five years.
By June, I will have lived here for five years.
Simple sums up the period and does not say that I will move away.
In June, I will have been living here for five years.
By June, I will have been living here for five years.
Continuous draws attention to the long period of living here; the main time facts are the same.
By then, I will have known my neighbour for ten years.
By then, I will have known my neighbour for ten years.
Know in the sense of “be acquainted with” describes a state, so the usual choice is Simple.
4. Number does not rule out Continuous
Distinguish between the number of completed results and the number of objects being worked on. Have edited three chapters sums up three edited chapters. Have been editing three chapters can describe working on these chapters in parallel without stating that they are all finished.
The question How many ...? often concerns the result, while How long ...? concerns duration. However, the meaning of the whole question matters, not just one word or number.
By Monday, I will have edited three chapters.
By Monday, I will already have edited three chapters.
Three is the number of results presented as complete.
By Monday, I will have been editing three chapters in parallel for a week.
By Monday, I will have been editing three chapters in parallel for a week.
Three is the number of objects being worked on; a week is the duration of the work. This is grammatically possible Continuous.
5. Do not add what the sentence does not say
Continuous does not guarantee that the process will continue after the stated point. That point may be the end of a shift, after which the person will stop working. Later events need to be stated separately.
Similarly, Continuous by itself confirms neither that the result is ready nor that it is not ready. If the “ready / not ready” status matters for a decision, add a separate, clear phrase.
When my shift ends at six, I will have been driving for eight hours. I will stop then.
When my shift ends at six, I will have been driving for eight hours. I will stop then.
A long process continuing up to six is entirely compatible with stopping afterward.
By Tuesday, we will have been testing the app for a week, but we will not have finished all the checks.
By Tuesday, we will have been testing the app for a week, but we will not have finished all the checks.
The second part states that the checks are unfinished; this is not communicated by the Continuous form itself.
6. A quick form check, including the passive
For Simple, use the third form of the verb after have: written, sent, finished. For Continuous, use been and the -ing form: been writing, been sending, been working.
Been does not always mean Continuous. The contract will have been signed is the correct Future Perfect in the passive: the contract will be signed. In They will have signed the contract, the people themselves sign the contract; the extra been would make the construction incorrect.
Simple: will have + V3; Continuous: will have been + V-ing; passive result: will have been + V3.
- verb / V —
- A word for an action or state, such as work or be. The pattern determines its form.
- V3 / past participle —
- The third verb form: worked, gone, seen. Used after have/has or in the passive, for example; it is not always the same as V2.
- V-ing / -ing —
- The verb form ending in -ing: working, going. Its role depends on the construction.
By Friday, they will have signed the contract.
By Friday, they will already have signed the contract.
Active construction: they are the people who sign.
By Friday, the contract will have been signed.
By Friday, the contract will already have been signed.
A passive result, not Continuous. After signed, there is no unnecessary direct object the contract.
7. Ask specifically for the information you need
To clarify the result, ask what or how many things will already have been done. To clarify the time spent, ask about the duration of the activity up to the same future point. Negating the result does not negate all the work either: “we will not have finished yet” does not mean “we will not have worked at all.”
In conversation, the full forms will not and I will and the contractions won’t and I’ll are natural in the appropriate style. After will in a question comes the subject, followed by have. In the time clause by the time you arrive, the future event is usually expressed with the Present Simple.
How many applications will you have reviewed by Thursday?
How many applications will you have reviewed by Thursday?
We are asking about the number of completed reviews, not the duration of the work.
How long will you have been reviewing applications by Thursday?
How long will you have been reviewing applications by Thursday?
We are asking about the accumulated duration of the activity.
I won't have reviewed them all by then.
I won't have reviewed them all by then.
The complete result is negated, but some applications may already have been reviewed.
Common mistakes
Incorrect:By Friday, they will have been signed the contract.
Correct:By Friday, they will have signed the contract.
We keep the active meaning: they will sign the contract. Been is unnecessary here; the correct passive would require a different structure, with the contract as the subject.
Incorrect:By noon, I will have been write for three hours.
Correct:By noon, I will have been writing for three hours.
After will have been, a form ending in -ing is needed for a continuing process, not the base form write.
Incorrect:By tomorrow, she will have wrote the summary.
Correct:By tomorrow, she will have written the summary.
In Simple, V3 written follows have, not the past-tense form wrote.
Incorrect:How long will have you been waiting by six?
Correct:How long will you have been waiting by six?
In the question, the subject you comes after will and before have.