How do you express future probability in English?

You stack a verb marker and, if you need extra grade, an adverb. Will and be going to sit at the sure end (She'll be at the annex by six; it's going to soak the terrace), should marks a reasonable expectation (The crossing should run), and may, might, and could leave the future open (The preview might still be cancelled). Probably, definitely, likely, and unlikely then fine-tune those choices.

What is the difference between will and might for the future?

Will treats the future as something you are willing to stand by: She'll text the berth number. Might treats it as an open chance: She might text if the signal holds. They are two points on a certainty scale, not two tenses, with could and may sitting with might and won't sitting with will as a committed negative. Adding definitely to will raises it further; adding definitely to might usually fights the meaning.

When do I use should for the future?

When you expect something because of a timetable, a pattern, or a plan, not when you are promising it. The crossing should run on the later tide means that is the reasonable forecast. I'll meet you at the annex is a commitment; I should meet you at the annex sounds like a weaker expectation or even like advice to yourself. Ought to does the same expectation job and keeps to.

Where do probably and definitely go in a future sentence?

After will in the affirmative: She'll definitely text. She'll probably wait. Before won't in the negative: She probably won't stay. After the first be with going to: She's probably going to wait. Likely is different: it is an adjective, so you need She's likely to wait or It's likely that she will wait, not She likely wait.

Is this the same as choosing will, going to, or the present continuous?

No. That choice, taught on the future-forms page, is about plans, evidence, decisions, and diary arrangements. Future probability is about how sure you sound once you are talking about later, and it brings in should, may, might, probably, and likely. You can use will for a certain prediction and also for an on-the-spot decision; the adverb and the context tell you which job it is doing.

English grammar · Intermediate

Future Probability: Will, Might, Should, and Likelihood

Written by Eleanor Whitfield, Lead English Curriculum Editor · Reviewed September 2026

Future probability is a scale, not a single tense. Will and won't sit at the ends (I am treating this as certain). Be going to can be almost as sure when present evidence is visible. Should marks a reasonable expectation. May and might sit in the maybe band. Probably, definitely, likely, and unlikely grade the same ideas from the adverb side. This is not the will versus going to versus present continuous choice (that is future forms), and it is not present deduction with must and can't.

She'll definitely text the berth number; the crossing might still be cancelled, but it should run on the later tide.

will plus definitely at the top of the scale; might lower down; should as a reasonable expectation

What it is

English does not have a dedicated future-certainty ending. It stacks a modal or a periphrastic future (will, be going to, should, may, might, could) and, if needed, an adverb (definitely, probably, likely). The speaker's commitment is the point, not the calendar. She'll definitely text is close to certain. The crossing should run on the later tide is what you expect from the timetable. It might still be cancelled is an open chance. Be going to with present evidence (Look at the sky: it's going to soak the terrace) is a high-probability prediction from what you can see now. The future-forms page decides which structure fits a plan, an arrangement, or a decision; this page decides how sure you sound once you are talking about later.

I'll be at the annex by six. (treated as certain) I should be at the annex by six. (reasonable expectation) I might be at the annex by six. (open chance) I'm likely to be at the annex by six. (adjective of probability plus to)

How to spot it

Look for a future time (later, tomorrow, at eight, on the later tide) plus a marker of how sure the speaker is. Will, won't, going to, should, may, might, could, probably, definitely, certainly, likely, and unlikely are the usual markers. Must for a future obligation (You must sign tomorrow) is not this scale; must for a present guess (That must be Maya) is present deduction.

She'll definitely text the berth number. (will plus definitely: top of the scale)
The crossing should run on the later tide. (should: reasonable expectation, not a promise)
The preview might still be cancelled if the kiln is firing. (might: open chance)
Look at those clouds: it's going to soak the terrace. (going to: high probability from present evidence)

Shall I and shall we are offers and suggestions, not probability. Will I is a rare future question about the speaker; more often we ask Shall I or Should I. Probability questions about other people use will, going to, or a modal: Will she text? Might the crossing be cancelled?

Future Probability Quick Reference

A working scale of future certainty

Marker	Commitment	Example
will / won't + definitely / certainly	treated as certain	She'll definitely text. She won't miss the cue.
be going to (present evidence or firm intention)	high, often visible now	It's going to soak the terrace. I'm going to take the dawn ferry.
should / ought to	reasonable expectation	The crossing should run on the later tide.
will probably / be likely to	probable, not locked	She'll probably wait in the wings. She's likely to wait.
may / might / could	possible, not probable	The preview might still be cancelled.
probably won't / unlikely to	probable that it will not happen	She probably won't stay for the encore. She's unlikely to stay.

Common Future Probability Examples in English

The same later event, different levels of commitment, so the scale is audible rather than listed:

High Certainty: Will, Won't, Going To

She'll be at the annex by six; the last bus is at ten past five.: will: treated as settled
She won't miss the cue; she has been marking it all week.: won't: treated as settled not-happening
Look at the sky: it's going to soak the terrace before the encore.: going to from present evidence
I'm going to take the dawn ferry, whatever the drizzle does.: going to as a firm prior intention

Will can also be a bare decision (I'll text you in a minute). On this page that decision sits at the certain end because the speaker is committing, not because the future is magically known.

Reasonable Expectation: Should, Ought To, Likely

The crossing should run on the later tide.: should: what the timetable leads you to expect
The kiln ought to have cooled by noon.: ought to: same job, a little more formal
She's likely to wait in the wings until the encore is cut.: likely to plus a base verb
The later ferry is likely to be quieter.: likely after be, grading a future state

Should as expectation is not should as advice (You should pack the scores tonight). If you can add if everything goes to plan, you have expectation. If you can add I recommend, you have advice.

Open Chance: May, Might, Could

The preview may overrun if the kiln is still firing.: may: a real possible later
The preview might still be cancelled.: might: a slightly more tentative later
We could be on the dawn ferry if this one fills.: could: a possible later option
It may not drizzle until we are off the quarry path.: may not: possible that it will not

These three overlap, as the may / might / could page explains. On a probability scale they occupy the same band, below should and above a bare guess with no marker at all.

Adverbs that Grade the Same Scale

She'll definitely text the berth number.: definitely next to will, high certainty
She'll probably wait in the wings.: probably: likely, not locked
She probably won't stay for the encore.: probably before won't in the negative
The crossing is unlikely to run after midnight.: unlikely to: probable non-event

Definitely and certainly sit next to the verb (She'll definitely text). Probably often sits there too in the affirmative, and before won't in the negative. Likely and unlikely are adjectives and usually need be plus to: She's likely to wait, not She likely wait.

How Future Probability Is Built

A modal or going to for the verb, an adverb or likely for the extra grade, and a negative that has its own order.

Choose a Verb Marker First

Will treats the future as something you are willing to stand by. Be going to treats it as already in train, or as readable from present signs. Should treats it as a reasonable expectation. May, might, and could leave it open. You can stop there; many sentences never add an adverb. Adding definitely to might (She might definitely come) fights itself and is rarely useful.

She'll text. She's going to text. She should text. She might text.

four verb markers, four levels of commitment

Pick the verb marker before the adverb.

Adverbs Sit Next to the Auxiliary, Not After the Whole Verb Phrase

Definitely, certainly, and probably usually come after will (She'll definitely text) and after be in going to (She's probably going to wait). In the negative, probably prefers a place before won't: She probably won't stay, which is more natural than She won't probably stay. Likely is not this kind of adverb; use be likely to.

She'll definitely text. She probably won't stay. She's likely to wait.

three different slots for three graders

Will + adverb + verb. Probably + won't. Be likely to.

Should as Expectation Is Weaker than Will

The crossing should run means I expect it to, given the usual pattern. It is the wrong marker for a promise or a decision (I'll text you, not I should text you, if you are committing). Ought to matches should here. Should have plus a participle is a different tense (past expectation or mild criticism) and is not future probability.

The kiln should have cooled by noon tomorrow.

should plus a future time, still an expectation

Should = I expect, not I promise.

Negatives Flip the Scale; They Do Not Use Don't May

Won't is high-certainty not-happening. Probably won't is weaker. Might not and may not leave a chance that it still happens. Shouldn't as expectation means I don't expect it to. True modals take not after them (might not, may not, should not); they never take do. Going to uses am/is/are not going to.

She won't miss the cue. She might not stay. She isn't going to wait in the rain.

three negative strengths, no do on the modals

Not after the modal. Do never appears.

Common Mistakes with Future Probability

Incorrect: She likely wait in the wings until the encore is cut.

Correct: She is likely to wait in the wings until the encore is cut.

Likely is an adjective and needs be plus to before a verb. Probably wait would also work (She'll probably wait) because probably is an adverb and can sit after will. Mixing the two patterns produces she likely wait, which is not a complete verb phrase.

Incorrect: The crossing might definitely be cancelled.

Correct: The crossing might be cancelled. / The crossing will definitely be cancelled.

Might and definitely pull in opposite directions on the scale. Pick the open-chance marker (might) or the high-certainty pair (will definitely), not both. The same clash appears in She may certainly come.

Incorrect: She won't probably stay for the encore.

Correct: She probably won't stay for the encore.

In the negative, probably prefers to sit before won't. She'll probably stay is the affirmative order; the negative does not simply insert not after that. Won't probably is heard, but probably won't is the standard written form.

Incorrect: The kiln should to have cooled by noon.

Correct: The kiln should have cooled by noon.

Should as a modal takes a bare verb, or have plus a participle, never to. Ought to is the cousin that keeps to: The kiln ought to have cooled. Mixing should with to is the have-to pattern applied to the wrong verb.

Will, Might, and Could as Future Markers

Full forms with wait, so the scale is visible in the same verb. Will sits at the certain end; might and could sit in the open-chance band. In speech, will contracts to 'll and will not to won't; might not and could not sometimes contract to mightn't and couldn't.

Will (treated as certain)

Will is the same for every person. The next verb is bare. Questions invert will.

Pronoun	Affirmative	Negative	Question
I	will wait	will not wait	Will I wait?
you	will wait	will not wait	Will you wait?
he / she / it	will wait	will not wait	Will she wait?
we	will wait	will not wait	Will we wait?
they	will wait	will not wait	Will they wait?

Contractions: I'll wait, she won't wait. Will she wait, not Does she will wait. Adding definitely or probably does not change the conjugation: she will definitely wait, she will probably wait.

Might (open chance, tentative)

Might does not change with person. It takes a bare verb and inverts in questions. Might is not a past tense here; it is a present modal about later.

Pronoun	Affirmative	Negative	Question
I	might wait	might not wait	Might I wait?
you	might wait	might not wait	Might you wait?
he / she / it	might wait	might not wait	Might she wait?
we	might wait	might not wait	Might we wait?
they	might wait	might not wait	Might they wait?

Contractions: she mightn't wait is possible, though might not is clearer in writing. Might she wait is grammatical but less common than Do you think she might wait.

Could (open chance or option)

Could as future possibility is also one form for every person. It is not past ability in this table. Could not wait in the future sense means it is possible that waiting will not happen, or that waiting will not be an available option; context decides.

Pronoun	Affirmative	Negative	Question
I	could wait	could not wait	Could I wait?
you	could wait	could not wait	Could you wait?
he / she / it	could wait	could not wait	Could she wait?
we	could wait	could not wait	Could we wait?
they	could wait	could not wait	Could they wait?

Contractions: she couldn't wait. Could she wait as possibility often sounds like a request or an offer; adding later or if this one fills keeps the probability reading: Could she wait for the dawn ferry if this one fills?

Probably, Definitely, Likely, and Won't

The adverb half of the scale, and the negative order that trips people.

Where the adverb sits

After will (She'll definitely text, She'll probably wait). Before won't (She probably won't stay). After the first be in going to (She's probably going to wait). Not after the whole phrase (not She'll text definitely in careful style).

She'll certainly make the dawn ferry.: certainly after will
She probably won't stay for the encore.: probably before won't
They're probably going to postpone the preview.: probably after are, before going to

Definitely won't is stronger than probably won't: She definitely won't miss the cue. The adverb still sits between subject and won't, or after will in the affirmative.

Likely and unlikely take be plus to

Likely is an adjective. The standard pattern is be likely to plus a base verb, or it is likely that plus a clause. She likely wait is not English. Odds are and chances are are informal cousins.

She's likely to wait in the wings.: be likely to plus base verb
It's likely that the crossing will run on the later tide.: it is likely that plus a clause
The midnight boat is unlikely to run.: be unlikely to

More likely and less likely are comparatives of the adjective: She's more likely to wait than to leave. That is still this scale, now graded.

Won't versus might not

Won't is a committed negative prediction or a refusal. Might not leaves a chance that the thing still happens. Don't confuse either with don't have to (no obligation) or must not (ban).

She won't miss the cue.: committed: I am treating this as certain not-happening
She might not stay for the encore.: open: staying may still happen
She isn't going to wait in the rain.: going to negative: plan or prediction against waiting

I won't wait can be a refusal rather than a prediction. The rest of the conversation usually makes that clear. Probability reading: given the drizzle, she won't wait on the quay.

Quick Check: Future Probability

Choose a marker that matches the degree of certainty in brackets.

1. She ___ definitely text the berth number. (certain)

Answer: will / 'll

will plus definitely at the top of the scale

2. The crossing ___ run on the later tide. (reasonable expectation)

Answer: should / ought to

should as expectation, not as advice

3. The preview ___ still be cancelled if the kiln is firing. (open chance)

Answer: might / may / could

maybe band

4. Look at those clouds: it ___ soak the terrace. (present evidence)

Answer: is going to / 's going to

going to from what you can see now

5. She ___ stay for the encore. (probable that she will not)

Answer: probably won't / is unlikely to / 's unlikely to

probably before won't, or be unlikely to

Future Probability FAQs

How do you express future probability in English?: You stack a verb marker and, if you need extra grade, an adverb. Will and be going to sit at the sure end (She'll be at the annex by six; it's going to soak the terrace), should marks a reasonable expectation (The crossing should run), and may, might, and could leave the future open (The preview might still be cancelled). Probably, definitely, likely, and unlikely then fine-tune those choices.
What is the difference between will and might for the future?: Will treats the future as something you are willing to stand by: She'll text the berth number. Might treats it as an open chance: She might text if the signal holds. They are two points on a certainty scale, not two tenses, with could and may sitting with might and won't sitting with will as a committed negative. Adding definitely to will raises it further; adding definitely to might usually fights the meaning.
When do I use should for the future?: When you expect something because of a timetable, a pattern, or a plan, not when you are promising it. The crossing should run on the later tide means that is the reasonable forecast. I'll meet you at the annex is a commitment; I should meet you at the annex sounds like a weaker expectation or even like advice to yourself. Ought to does the same expectation job and keeps to.
Where do probably and definitely go in a future sentence?: After will in the affirmative: She'll definitely text. She'll probably wait. Before won't in the negative: She probably won't stay. After the first be with going to: She's probably going to wait. Likely is different: it is an adjective, so you need She's likely to wait or It's likely that she will wait, not She likely wait.
Is this the same as choosing will, going to, or the present continuous?: No. That choice, taught on the future-forms page, is about plans, evidence, decisions, and diary arrangements. Future probability is about how sure you sound once you are talking about later, and it brings in should, may, might, probably, and likely. You can use will for a certain prediction and also for an on-the-spot decision; the adverb and the context tell you which job it is doing.