Since vs For: What's the Difference?
Use for with a length of time and since with the point in time it started.
Word Origins & Etymology
For here marks duration — how long something lasts. It answers "for how long?" with an amount of time.
Since comes from Old English siththan, "after that," and marks a starting point — the moment a still-continuing situation began. It often pairs with the present perfect.
For + a period (for two hours). Since + a point (since noon). If you can count it as a length, use for; if it names when it began, use since.
⚡ Quick Answer
Use since with a starting point: "since 2020," "since Monday," "since I was a child."
Memory Trick: Since points to the start (both begin with S). For covers the full stretch of time (both have an F-ish "full" feel).
🔑 Key Takeaway
Ask: am I naming a duration or a start? Duration → for (for ten minutes). Start → since (since 9 a.m.). Both often use the present perfect.
| Word | Follows with | Example | Answers |
|---|---|---|---|
| For | A period of time | "for six months" | How long? |
| Since | A point in time | "since June" | Starting when? |
| Since | A clause (start event) | "since I moved here" | Starting when? |
Quick Comparison
| Form | Use It For | Quick Check |
|---|---|---|
| For | A length/duration of time | Could you put a number of units after it (for 5 days)? Use for. |
| Since | The point the situation began | Does it name when it started (since Friday)? Use since. |
| Since (because) | Giving a reason | Could you replace it with because? That is the other since. |
When to Use "For"
Use for with a stretch of time — a number of seconds, minutes, hours, days, years, or vaguer amounts like "a while."
- We have lived here for ten years.
- She talked for an hour.
- I haven’t seen him for a long time.
When to Use "Since"
Use since with the point in time a situation started — a date, day, clock time, or an event clause. It typically appears with the present perfect.
- We have lived here since 2014.
- I have been awake since 5 a.m.
- She has changed since she started the new job.
Two notes: "since" can also mean because ("Since you’re here, let’s start"). And both for/since usually go with the present perfect for situations that continue to now.
The Other "Since": Because
Outside of time, since has a second job — giving a reason, like because: "Since you are here, let us start." Context makes the meaning obvious. For time, pair for and since with the present perfect ("have lived") or present perfect continuous ("have been living") when a situation continues to now. And do not confuse since with ago: "two years ago" marks a point in the past, while "for two years" describes the stretch up to the present.
Common Mistakes
Mistake #1: "since three years"
✗ Wrong: I have worked here since three years.
✓ Right: I have worked here for three years.
Reason: Three years is a duration, so use for.
Mistake #2: "for last Monday"
✗ Wrong: She has been ill for last Monday.
✓ Right: She has been ill since last Monday.
Reason: Last Monday is a starting point, so use since.
Mistake #3: simple past with since-duration
✗ Wrong: I know him for five years.
✓ Right: I have known him for five years.
Reason: An ongoing situation up to now uses the present perfect.
Mistake #4: "since 2 hours"
✗ Wrong: We have waited since two hours.
✓ Right: We have waited for two hours.
Reason: Two hours is a length of time, so use for.
🎯 Test Your Knowledge
1. They have been married ____ 2010.
2. I have studied English ____ five years.
3. He has been here ____ this morning.
4. We talked on the phone ____ an hour.
5. She has felt better ____ she changed her diet.
See It Live: Our Engine Flags a Real Mistake
Below runs Grammarlyzer’s live engine, not an image. The starter sentence uses since with a duration; correct it or paste a sentence of your own.
Expected correction: I have worked at this company for five years.
Honest limits: the engine catches many since/for slips, but the choice depends on whether you mean a duration or a starting point. Decide which, then run the check.
Frequently Asked Questions
When do I use "for" and when "since"?
Why is "since five years" wrong?
Do for and since always need the present perfect?
Can "since" mean "because"?
What follows "since"?
Real-World Examples
She has led the team since January.
We have lived in Seoul for six years.
The theory has been debated since the 1990s.
I have been waiting for twenty minutes.
He has felt better since the surgery.
They have traveled for three months.
I have known her since ten years.
We have been here for last week.
Why Since and For Get Mixed Up
Many languages use one preposition for both duration and starting point, so learners pick whichever feels familiar. Because both often appear with the present perfect, the surrounding grammar looks the same, hiding the error. The reliable test is what follows the word: an amount of time means for; a moment it started means since.
Since vs for lives inside the present perfect. Master the tense itself in present perfect vs simple past, then keep tenses aligned with tense consistency.
Related Articles
- Present Perfect vs Simple Past — The tense that for and since most often use
- Tense Consistency — Keep time references aligned across a sentence
- Time Progression Words — More connectors for sequencing time
- Used To vs Would — Another way to talk about time and habits
- ← View All Grammar Guides
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