Both words talk about time, so learners swap them all the time. But they answer two different questions.
- Since gives the starting point: when did it begin?
- For gives the length of time: how long has it lasted?
Since: the starting point
Use since with a moment in time, such as a day, a date, a time or an event. It looks back to the start.
I've lived here since 2020.
We've been waiting since nine o'clock.
Mia has been my friend since Monday.
Leo hasn't eaten since breakfast.
It's been quiet since the teacher left.
After since you can have a time (Monday, 2020, last summer), an event (my birthday, the party) or a short clause (since I was six, since she moved).
For: the length of time
Use for with an amount of time: how long something has lasted.
I've lived here for four years.
We've been waiting for two hours.
Mia has been my friend for a week.
Leo hasn't eaten for a long time.
It's been quiet for ten minutes.
After for you have a number and a time word (three days, two weeks, ten minutes) or a general amount (a long time, ages, a while).
They can say the same thing
The same fact can use either word:
I've played the piano since I was six.
I've played the piano for four years.
One names where the time started, and the other measures how long it has lasted.
Easy way to tell them apart
Ask: am I naming a moment, or measuring an amount?
- A moment (Monday, 2020, my birthday): use since.
- An amount (three days, two years, a long time): use for.
💡 The OddLingo Trick
Since starts. For goes the full length.
Think of a ruler. Since points to the zero at the left end, where it began. For measures along the whole ruler: how far it went.
⚠️ Common mistakes
A moment needs since.
❌ I've known her for 2019.
✅ I've known her since 2019.
An amount needs for.
❌ I've been here since three hours.
✅ I've been here for three hours.
Use a perfect tense for time up to now.
❌ I live here since Monday.
✅ I have lived here since Monday.
Good to know
Since has another meaning: because. Since it's raining, we'll stay inside. There is no time idea here.
The tense in the "up to now" use is usually present perfect: have lived, has been, haven't seen. That is why I live here since Monday sounds wrong.
💬 In a conversation
Sam: How long have you been here?
Mia: Since lunch.
Sam: That's not a number.
Mia: It's a start. Okay: for two hours.
Sam: What have you been doing?
Mia: Waiting for you, since I got here.