The Most Common Time Grammar Mistake
Ask almost any English learner what they find difficult, and since vs. for will be on the list. Both are used to talk about time — but they follow very different rules. Once you understand the core difference, you'll get it right every single time.
The Core Difference
- For is used with a duration — a length of time (how long something has lasted).
- Since is used with a point in time — a specific moment when something started.
The key question to ask yourself is: "Am I talking about how long, or when it started?"
Using "For" — A Duration of Time
Use for when you describe a period or amount of time:
- I have lived here for three years.
- She studied English for six months.
- We've been waiting for a long time.
- He worked at that company for a decade.
Notice that for is always followed by words that describe a length: three years, six months, a long time, two weeks, etc.
Using "Since" — A Point in Time
Use since when you name the specific moment something started:
- I have lived here since 2022.
- She has studied English since January.
- We've been friends since high school.
- He hasn't called me since last Tuesday.
Notice that since is always followed by a specific point: a year, a month, a day, a life event.
Comparison Table
| For (Duration) | Since (Point in Time) |
|---|---|
| for two hours | since 9 o'clock |
| for a week | since Monday |
| for three months | since March |
| for many years | since 2010 |
| for a long time | since I was a child |
Which Tense Goes with Since and For?
Both since and for are most commonly used with the present perfect tense (have/has + past participle) when talking about situations that started in the past and are still true now.
✅ "I have known her for five years." (Still know her now)
✅ "I have known her since 2020." (Still know her now)
You can also use for with the simple past when something is finished:
✅ "I lived in Tokyo for two years." (I don't live there anymore)
❌ "I lived in Tokyo since 2010." — This is incorrect with simple past.
Common Mistakes to Avoid
- ❌ "I have been here since three hours." → ✅ "...for three hours."
- ❌ "She has worked here for last year." → ✅ "...since last year."
- ❌ "We've known each other since a long time." → ✅ "...for a long time."
Quick Test
Choose for or since:
- "I haven't eaten _____ this morning." → since
- "She has been learning guitar _____ two years." → for
- "They've been married _____ 1998." → since
- "We talked on the phone _____ an hour." → for
Remember the rule: for = how long, since = when it started. Keep that in mind and you'll never mix them up again!