Why do so many learners mix these up?

Because most European languages use one word where English uses two. German seit, French depuis, Spanish desde and Italian da all cover both a starting point and a duration, so there is nothing in the first language to split. The fix is to check what follows the word rather than to translate it.

Often, in positive statements: I’ve lived here ten years is natural. Keep it in negatives and questions, where dropping it sounds wrong, I haven’t seen him for weeks needs it. Since can never be omitted.

Does since always mean time?

No. It also means because, usually at the start of a sentence, since you’re here, could you help? That use has nothing to do with duration and takes ordinary tenses, so it will not interact with the present perfect rule at all.

Which one to useA2

Since vs for

The short answer

For takes a length of time: for three years, for ten minutes. Since takes the point it began, since 2019, since Monday, since I moved here. Both normally require the present perfect, and using a present tense with them is the error that outlasts the since-or-for choice itself.

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At a glance

For or Since?

Compare	ForA length of time.	SinceThe point it started.
What follows it	A duration: two hours, ages	A start point: Monday, 2019, this morning
Answers	How long?	Starting when?
Can follow a clause	No	Yes, since I got here
Usual tense	Present perfect	Present perfect, almost always
With the past simple	Possible: I lived there for a year	Rare, and usually wrong
Other meanings	Purpose: this is for you	Because, since you asked

How to choose

Ask these, in order

1
Is what follows a length of time?
For. Two days, six months, a while, ages, a long time.
I’ve known her for fifteen years.
Fifteen years is a length.
2
Is it a point on the calendar or the clock?
Since. Monday, 8 o’clock, March, 2019, last week.
She’s been off work since Tuesday.
Tuesday is a point, not a duration.
3
Is it a whole clause, an event that marks the start?
Since, and the clause usually goes into the past simple.
We haven’t spoken since he moved to Lisbon.
The moving is a past event; the not speaking continues.
4
Is the situation still true now?
Present perfect in the main clause, whichever word you chose.
I’ve worked here since January. / I’ve worked here for eight months.
Same situation, two ways of measuring it.

Side by side

Each one, in full

For

When to use for

A length of time.

For measures the length of the period. Anything you could put a number and a unit on takes for: for three days, for two minutes, as do vague durations like for ages and for a while.

For is the more flexible of the two with tenses. It works with the past simple for a finished period (I lived in Madrid for two years, and no longer do) and with the present perfect for one that continues, so the tense you pick changes the meaning rather than being forced.

They’ve been married for thirty years.

And still are.

I waited for twenty minutes and then left.

Finished period, past simple.

NBSince could not appear here at all.

We haven’t seen them for ages.

An indefinite length.

Since

When to use since

The point it started.

Since names the moment the situation started. That can be a date, a day, a clock time, or a whole clause describing an event, since I started this job, since we last met.

Because since inherently connects the past to now, it very rarely works with the past simple. If you find yourself writing “I lived here since 2019”, the fix is the tense rather than the preposition.

It’s been raining since about six.

A clock-time starting point.

She hasn’t called since the weekend.

A point on the calendar.

A lot has changed since I was last here.

A clause as the starting point.

NBThe clause goes into the past simple; the main verb stays in the perfect.

Mistakes to avoid

What learners actually get wrong

I live here since 2020.
I’ve lived here since 2020.
Since needs a tense that reaches from the past to now, and the present simple does not. French, Spanish, German and Italian all use a present here, so this transfers directly and survives to advanced levels.
I’ve been waiting since two hours.
I’ve been waiting for two hours.
Two hours is a length, so it takes for. This one comes straight from languages that use a single word for both, German seit and French depuis cover the whole range that English splits.
How long time have you been here?
How long have you been here?
How long already contains the idea of duration, so adding time is redundant. The answer can use either word: for two years, or since 2024.
I have worked there for three years, but I left in 2022.
I worked there for three years, but I left in 2022.
For does allow the past simple, and here it is required, the job is over. This is the one case where for and since genuinely diverge in what tenses they permit.

Now use it

Present perfect

for, since, just, yet, already, ever: the words that pick the tense. Reading a rule and being able to apply it are different skills, and only one of them shows up when you speak.

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Questions

Asked and answered

Why do so many learners mix these up?: Because most European languages use one word where English uses two. German seit, French depuis, Spanish desde and Italian da all cover both a starting point and a duration, so there is nothing in the first language to split. The fix is to check what follows the word rather than to translate it.
Can for be left out?: Often, in positive statements: I’ve lived here ten years is natural. Keep it in negatives and questions, where dropping it sounds wrong, I haven’t seen him for weeks needs it. Since can never be omitted.
Does since always mean time?: No. It also means because, usually at the start of a sentence, since you’re here, could you help? That use has nothing to do with duration and takes ordinary tenses, so it will not interact with the present perfect rule at all.

Keep going

Past simple vs present perfectB1Look at the time, not the event.