Since and For

The use of FOR

We use For when we measure the duration – when we say how long something lasts.
For + a period of time
To measure a period of time up to the present, we use the present perfect tense and not the present tense.

• I have known her for a long time. (Correct)
  I know her for a long time. (Incorrect)
• I have lived here for ten years. (Correct)
  I live here for ten years. (Incorrect)

The present tense with For refers to a period of time that extends into the future.

• How long are you here for? (Until when)
• How long have you been here for? (Since when)

In reality, we can use all verb tenses with For.

However, we don't use For with expressions such as all day or all the time.

• I was there all day. (Correct)
• I was there for all day. (Incorrect)

The use of SINCE

Since gives the starting point of actions, events or states. It refers to when things began.
Since + a point in time (in the past), until now.

• I've been waiting since 7 o'clock.
• I have known him since January.

With since we use the present perfect tense or the past perfect tense.

• I have been here since 5 o'clock and I am getting tired.
• I had been working since 5 o'clock and I was getting tired.

Since can also be used in the structure It has been + period of time + since.

• It has been two months since I last saw her.
• It has been three years since the last earthquake.