Depuis and pendant are very similar in meaning and both often are translated as "for" in English. This can be very confusing.

Both denote the length of an interval, but depuis can't be used for intervals in the future, only those that end either in the past or reach up to the present moment. With a specific point of time mentioned, depuis can also mean "since", not only "for".

Je vis en France depuis 3 ans. -- I've lived in France for 3 years. (And I'm still living there at the moment.)
Je vis en Frence depuis 2017. -- I have been living in France since 2017.

Pendant works for all intervals but has no relation to the present and can't be used to mean "since".

Je serai à Paris pendant une semaine. -- I will be in Paris for 1 week. (Can't use depuis because the interval is in the future.)
J'ai vécu en France pendant 6 mois. -- I lived in France for 6 months. (But not anymore, since pendant has no relationship to the present.)

Hi Daralyn,

I think the point to understand is just what does each preposition express?

Pendant  --> during which time, dans / pour

Depuis  --> from, since - during the following ....

Hope this helps.

Jim