When or if? Time and condition
Short answer: When tells the time of something: When I was five, I started school. If tells what must happen first: If it rains, we will stay home. After if, use the present tense for the future, and put will in the main part. Put a comma after the when or if part when it comes first, and do not add so.
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At a glance
| Word | Meaning | Pattern | Example |
|---|---|---|---|
| when | time | When + idea, main idea | When I was five, I started school. |
| if (real future) | condition | If + present, will + verb | If it rains, we will stay home. |
| if (always true) | fact | If + present, present | If you heat ice, it melts. |
In short
- when = time. if = condition.
- After if use the present. will goes in the main part.
- A comma after the when / if part when it comes first. No so.
What is the rule for “when and if”?
The rule
when joins a time. if joins a condition: if A happens, B happens.
How it looks
When + idea, main idea · If + present, will + action word
What it means
when says the time. if says what must happen first.
When to use it
Use them to join two ideas about time or a condition.
How it works
- Is it about time? Use when. Is it a condition, something that might happen? Use if.
- After if, use the present: If it rains... not If it will rain.
- Put will in the main part: ..., we will stay home.
- Put a comma when the when or if part comes first. No comma when it comes last.
Examples of “when and if”
- When I was five, I started school.
The when part first: comma. - I feel happy when I play.
The when part last: no comma. - If it rains, we will stay home.
If + present, will + action word. - If you heat ice, it melts.
A fact that is always true: both parts in the present. - I will call you when I arrive.
when I arrive: after the main part, so no comma. - If you study, you will pass.
If + present, will + verb. - When the bell rings, we go home.
when for a repeated time. - If I see him, I will tell him.
If + present, will + verb.
Common mistakes with “when and if”
If it will rain, we stay at home.→ If it rains, we will stay at home.
After if use the present. will goes in the main part.When I was five, so I started school.→ When I was five, I started school.
No so after the when part.If it rains we will stay at home.→ If it rains, we will stay at home.
A comma after the if part.When I will arrive, I will call you.→ When I arrive, I will call you.
After when, use the present for the future.If it rains, so we stay at home.→ If it rains, we stay at home.
No so after the if part.
Exceptions: watch out
- A fact
For things that are always true, use the present in both parts: If you heat ice, it melts.
When or while? If or unless?
When is for a point in time. While is for a longer action. If is for a condition. Unless means if not.
| Word | Meaning | Example |
|---|---|---|
| when | at that time | When I arrived, it was raining. |
| while | during that action | While I was cooking, he called. |
| if | on condition | If you hurry, you will catch it. |
| unless | if not | You will miss it unless you hurry. |
See also: unless
Check yourself
- Fix: “If it will rain, we stay in.”
Show the answer
If it rains, we will stay in. Present after if; will in the main part.
- Fix: “When I was ten, so I moved.”
Show the answer
When I was ten, I moved. No so after a when part.
- Choose: “___ I see her, I will say hello.” (When / If)
Show the answer
When It is certain; use when for sure events.
How to practice “when and if”
The interactive version adds step-by-step help, spoken instructions and a quick check. One rule card, one sound lesson and the first lesson of every stone are free to try; the rest is part of Full Access. See Full Access.
- Practice lesson: when and if
Questions
When do I use “when” and when “if”?
Use when for something certain to happen: When I get home, I will eat. Use if for something that may or may not happen: If I get home early, I will cook.
Do I need a comma?
Yes when the when or if part comes first. No comma when it comes second.
Can I put will after if?
In requests it is sometimes possible, such as If you will wait, I will help. For normal future conditions, use the present.
More Grammar in Context rules
- The best: comparing three or more: To say which one is number one, use the + -est, or the most for long words.
- Future: will and won't: will talks about the future. After will, use the plain action word.
- Plans: am / is / are going to: Use am, is or are + going to + the plain action word for plans, and for things we can see coming.
- Telling a story: first, then, next, finally: Order words put the steps of a story in order. Keep the whole story in the past.
- Polite talk: Can I …? Would you like …?: Ask with Can I have … , please? Offer with Would you like …? Answer with Yes, please or No, thank you.
- always, usually, sometimes, never: Words like always and never tell how often. They go before the action word but after am / is / are.
Used in these writing topics
Part of the 📘 Grammar tool. Level G4: Grammar in Context. Đọc bằng tiếng Việt.
Written for English learners by the English for Fun team. How we write our lessons · Last updated 2026-11-05.
Reviewed by Chinh Q. Hoang, PhD, founder, English for Fun · 2026-10-30
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