Since and For: Difference, Rules, and Examples

Use for to talk about a duration. Use since to talk about a starting point in time.

That’s the key difference.

Many English learners confuse these two words because both are used with time expressions, especially in the present perfect tense. But the choice becomes simple once you focus on what comes after the word.

• If you’re talking about how long, use for.
• If you’re talking about when something started, use since.

Compare:

• I have lived here for five years.
• I have lived here since 2019.

In this guide, you’ll see clear explanations, practical examples, common mistakes to avoid, and short practice exercises to help you use both words confidently.

When to Use “Since”

Use since to show the exact point in time when something started.

If the sentence answers the question “Since when?”, you need since.

Since is followed by:

• A year → since 2020
• A date → since March 5
• A time → since 8 a.m.
• An event → since I graduated
• A clause → since she moved here

Examples

• She has worked here since 2018.
• I have known him since high school.
• We have lived in this city since January.
• He has been tired since he woke up early.

In all of these sentences, since introduces the starting moment of the action.

Important: Tense Matters

Since is most commonly used with the present perfect tense and the present perfect continuous because the action started in the past and continues now.

• I have lived here since 2019.
• She has studied English since she was a child.

You normally do not use since with a simple duration like “two hours.” That would be incorrect.

Incorrect:

• I have waited since two hours.

Correct:

• I have waited for two hours.

When to Use “For”

Use for to show the length of time something lasts.

If the sentence answers the question “For how long?”, you need for.

For is followed by:

• A number + time unit → for three days
• A duration → for a while
• A period of time → for many years

Examples

• I have lived here for five years.
• She has worked at the company for two months.
• We waited for an hour.
• He studied English for a long time.

In each sentence, for introduces a duration, not a starting point.

Tense Flexibility

Unlike since, for can be used with more than one tense.

With present perfect (action continues):

• I have lived here for five years.

With simple past (action finished):

• I lived there for five years.

That’s an important difference. Since usually connects to a starting point, while for works naturally with completed periods as well.

For and Since Common Mistakes

Most errors happen when learners mix up a duration and a starting point.

If you clearly identify whether you are talking about how long or since when, you can avoid almost every mistake.

1. Using “since” with a duration

Incorrect:

• I have lived here since five years.
• She has waited since two hours.

Why it’s wrong: “Five years” and “two hours” describe a length of time, not a starting moment.

Correct:

• I have lived here for five years.
• She has waited for two hours.

2. Using “for” with a starting point

Incorrect:

• I have worked here for 2019.
• She has known him for January.

Why it’s wrong: “2019” and “January” are specific points in time.

Correct:

• I have worked here since 2019.
• She has known him since January.

3. Using the wrong tense with “since”

Incorrect:

• I live here since 2020.

Correct:

• I have lived here since 2020.

Because since usually connects a past starting point to the present, it commonly appears with the present perfect tense.

Since = Because (Not Time)

“Since” does not always refer to time. It can also mean “because.”

This is a common source of confusion. When since means because, it introduces a reason — not a starting point in time.

Since (time)

• I have lived here since 2020.
• She has worked here since January.

Here, since shows when something started.

Since (because)

• Since it was raining, we stayed home.
• I left early since I was tired.

In these sentences, since means because. It explains why something happened.

How to Tell the Difference

Try this quick test:

If you can replace since with because, it is not about time.

• Since it was late, we went home.
• Because it was late, we went home.

If the sentence does not make sense with because, then it probably refers to time.

Quick Practice: Since or For?

Choose since or for in each sentence.

Try to decide by asking yourself: Is this a starting point or a duration?

Fill in the blanks

1. I have lived here ______ 2015.
2. She has worked at the company ______ three years.
3. We have known each other ______ high school.
4. He has been sick ______ two days.
5. They have studied English ______ January.
6. I waited ______ an hour.
7. She has stayed here ______ Monday.
8. We have traveled together ______ a long time.

Answer Key

1. since
2. for
3. since
4. for
5. since
6. for
7. since
8. for

Conclusion

The difference between since and for comes down to one simple idea: starting point vs duration.

Use since when you mention when something began. Use for when you describe how long something lasts.

If you remember to ask yourself “since when?” or “for how long?”, you’ll choose the correct word almost every time.

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