"Since" vs "for" with the present perfect - explained

One refers to a point in time, the other to a length of time.

Both "since" and "for" appear all the time with the present perfect, and mixing them up is one of the most common errors learners make. The good news is that the rule is simple once you know what each word answers.

• "I've lived here for three years."
• "She's been waiting for an hour."
• "We've worked together for a long time."
• "They've known each other for decades."
• "I haven't seen him for ages."

For is followed by an amount of time: minutes, hours, days, weeks, months, years, a long time. If you can count the length of the period, "for" is your word.

• "I've lived here since 2021."
• "She's been waiting since nine o'clock."
• "We've worked together since we were students."
• "He's been off work since Monday."
• "I haven't spoken to her since the wedding."

Since is followed by a specific moment: a year, a date, a time, or an event. Notice in "since we were students" and "since the wedding" that the starting point can be a whole event, not just a clock time.

• How long? → for
• When did it start? → since

Think "Since points to a Start." Both begin with an S. "For" measures a full stretch of time, so picture a ruler measuring the whole length.

• "I've been here since three hours." ✗ → "I've been here for three hours." ✓
• "I've been here for 2019." ✗ → "I've been here since 2019." ✓
• "I know her for five years." ✗ → "I've known her for five years." ✓

That last mistake is worth noting. Both "since" and "for" in this sense pair naturally with the present perfect, not the present simple, because you are describing something that started in the past and continues now. Saying "I know her for five years" is a very common slip for learners whose first language uses the present tense here.

"Since you're here, we can start." This is a different use entirely, don't confuse them. In this meaning "since" introduces a reason, and it does not need the present perfect at all. "Since it was raining, we stayed indoors" works perfectly well. Context makes the meaning clear, but keep the two uses separate in your mind.

Good news here. There is no difference between British and American English with "since" and "for" in this context. Both varieties follow exactly the same rule, so you can use these words with confidence wherever you are.

The grammar stays identical, but the vocabulary around it shifts. In a professional email you might write, "I have been with the company for eight years" or "We have partnered since 2015." In casual speech you are more likely to hear contractions and looser time markers, such as "I've been stuck here for ages" or "We've been mates since school." The structure never changes, only the tone.

"Ago" also talks about time, but it works differently. "Ago" counts back from now to a finished point and pairs with the past simple, not the present perfect. Compare "I moved here three years ago" (past simple, a completed action) with "I have lived here for three years" (present perfect, still true now). Learners sometimes blend these, so remember that "ago" looks back to a finished moment while "for" and "since" connect the past to the present.

Both are neutral and universal. Important in all written and spoken English.