Grammar › Conditionals › If vs When
If vs When
Both link a future condition to a result, but they differ in certainty:
- if — a possibility that may not happen (If I have time, I'll help).
- when — a certainty; only the time is open (When I finish, I'll rest).
After if and when, use the present simple for the future — never 'will': When it starts, not 'when it will start'.
if vs when
| Word | Certainty | Example |
|---|---|---|
| if | it may or may not happen | If it rains, we’ll stay in. |
| when | it will definitely happen (timing unknown) | When I get home, I’ll call you. |
Both use the present simple (not ‘will’) in the if/when clause.
When to use each
1. if — a possibility
- If I pass the exam, I’ll celebrate. (I might not pass)
- If you need help, just ask.
2. when — a certainty
- When the film ends, we’ll get dinner. (the film will end)
- I’ll text you when I arrive.
3. when = whenever (repeated)
- When I drink coffee at night, I can’t sleep. (a general pattern)
⚠️ Compare: I’ll call you if I finish early (maybe I won’t) vs I’ll call you when I finish (I will finish; just not sure when).
Common mistakes
1. ‘will’ after if/when. When I will arrive → When I arrive.
2. ‘when’ for something uncertain. When I win the lottery, I’ll travel (unlikely) → If I win the lottery, I’ll travel.
3. ‘if’ for a certainty. I’ll retire if I’m 65 → I’ll retire when I’m 65 (you will reach 65). Pro tip: if = maybe; when = definitely (only the time is open).
✏️ Practice: If vs When
1. ___ the sun goes down, it gets cold here. (certain)
2. ___ it rains tomorrow, we'll cancel the picnic. (uncertain)
3. I'll call you ___ I get to the airport. (certain arrival)
4. ___ you need anything, just let me know. (possible)
5. Choose the present simple: 'When it ___ , I'll open the window.'
6. We'll move to a bigger house ___ the baby is born. (certain)
7. ___ I win the competition, I'll be amazed. (unlikely)
8. ___ I drink coffee late, I can't sleep. (a general pattern)
9. Correct this: 'When I will finish work, I'll come over.'
10. Which word shows the event is CERTAIN, only the time is unknown?
Frequently asked questions
What's the difference between 'if' and 'when' for the future?
'If' shows something is possible but uncertain (If he calls, tell him). 'When' shows it's certain to happen; only the timing is unknown (When he calls, tell him).
Do I use 'will' after if and when?
No. Use the present simple in the if/when clause: When I see her, I'll ask (not 'when I will see her').
Can 'when' replace 'if' in the first conditional?
Only if the event is certain. 'When the sun rises' (certain) vs 'If it rains' (uncertain) — you can't swap these.
Is 'when' ever like 'whenever'?
Yes, for repeated situations: When (= whenever) I'm tired, I drink coffee — a general truth similar to the zero conditional.
👩🏫 For teachers
CEFR objectives for “If vs When”:
- Can choose 'if' (possible) or 'when' (certain) for future events (CEFR B1).
- Can use the present simple after if/when for the future.
- Can recognise 'when' meaning 'whenever' for repeated situations.
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