For and since are two English prepositions that we can use to talk about time in English. They are similar, but we use them a little differently (Be careful! For and since have other meanings as well).

Which verb tenses do we use with for and since

We can use these words with many different verb tenses, especially these ones:

Many learners try to use for and since with the simple present, but this is usually an error:

I am living in Medellin since 2011

I study English for 3 hours

There are some exceptions, but generally you want to use the present perfect or present perfect continuous in to describe an action or situation that started in the past and is still true:

I have lived in Medellin since 2011

I have been studying English for 3 hours

The Difference Between For and Since

Here is the important difference between for and since: We use for with an amount of time, but we use since with a point in time.

Using For

We use for to express an amount of time (we could also call this a period or time or a duration). Here are some examples of for with amounts of time:

for two years

for 3 hours

for a week

for a long time

for a little while

for centuries

for ages

for as long as I can remember

Using Since

We use since with a point in time, the time when an action or situation began.

since last week

since Monday

since December 11

since September

since 1984

since Thanksgiving

since last fall

since I was born

Ago

Ago is a useful word for changing most durations into points in time. That is, two years is a duration and we use it with for. But if we add ago, two years ago is a point in time, and we can say since two years ago. Here are some examples with ago:

since five years ago

since 3 hours ago

since a week ago

Note that using since with ago is a little informal, and better for speaking than formal writing.

Chart For and Since with Verbs in English