When do you use 'since' and when do you use 'for' with the present perfect?

The key difference: One refers to a point in time, the other to a length of time.

• "I've lived here for three years."
• "She's been waiting for an hour."
• "We've worked together for a long time."

For is followed by an amount of time: minutes, hours, days, weeks, months, years, a long time.

• "I've lived here since 2021."
• "She's been waiting since nine o'clock."
• "We've worked together since we were students."

Since is followed by a specific moment: a year, a date, a time, or an event.

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

• "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." ✓

"Since" can also mean "because": "Since you're here, we can start." This is a different use entirely - don't confuse them.

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

Tags: grammar, tense, present perfect, common mistakes, since vs for