(1)  How long have you(been………?)

• How long have they been married?( we do not say, ” How long are they married? “)
• They have been married for 25 years.( we do not say, ” They are married for……)
• He has been in hospital since Saturday.( We do not say, ” He is in hospital……..)
• I have been learning English for a long time. ( we do not say, ” I am learning …….)
• I like your house.  How long have you been staying here?
• I have been staying here for the last 10 years.
• How long have you known him?
• I have known him since we were at school.
• I haven’t seen him since Wednesday.
• The boy has been missing since last Friday.
• How long have they been studying in this school?
• They have been studying in this school since 2001.

Note :  Some verbs ( for example, know/like/believe etc) are not normally used in the continuous.  And after ‘ How long ….’ either present perfect tense OR present perfect continuous tense is used as the case may be.  But present tense OR present continuous tense should not be used after ” How long”.  However in Spoken English some relaxation( regarding the rules) can be made if the situation warrants.

(2) How long is it since…………….? (Note : in this particular usage , the part of the sentence that comes after the word ‘ Since ‘ should be in the simple past.)

• How long is it since you last saw him? ( i.e when did you last see him?)
• I saw him last in 1999.
• How long is it since he died? ( when did he die?)
• It’s ten years since he died.
• It’s two years since I last saw him.( i.e I haven’t seen him for two years)
• It’s ages since we went to the cinema.( i.e we haven’t been to the cinema for ages)